Reflective Optical Encoder Capitalizing on an Index Grating Imbedded in a Compact Smart Frame

Abstract

A reflective optical encoder has been proposed and realized capitalizing on a miniaturized sensing head, which integrates both a pair of index gratings and a beam router in a plastic smart frame. The index gratings play a role in selectively transmitting the incident beam carrying the periodic grating pattern of a code scale. The beam router, consisting of a collimating lens in conjunction with a prism, is used to collimate and steer the beam originating from a vertical-cavity surface-emitting laser (VCSEL) toward the code scale. The proposed encoder is rigorously designed by ray optic simulations and manufactured by passively aligning a smart frame, which is produced by plastic injection molding, with a VCSEL at ¼ 850 nm and two semicircular photodetectors. The index grating is created by forming an Al grating pattern of a 10-m pitch on a silica substrate. Two output signals provide sinusoidal signals, which are 90 out of phase from each other. The period of the signals is 4 s at a frequency of 250 kHz, which is equivalent to a period of 10 m. As expected, the relative phase relationship is reversed by altering the direction of rotation of the code scale. By examining either of the two output signals, we can simply demonstrate positional and angular resolutions of about 10 m and 0.04 , respectively. The attained resolutions can be readily enhanced to 2.5 m and 0.01 , by simultaneously taking into account the two signals with a distinct 90 phase difference.

Calibration of non-contact incremental linear encoders using a macro–micro dual-drive high-precision comparator

“…encoders. On the one side, the encoders employ new configurations with more advanced elements so as to deliver superior count accuracy along with compact package dimensions [5][6][7]. On the other side, the utilization of more efficacious signal processing methods brings in stronger processing power, a higher resolution and higher alignment tolerances [8][9][10].…”

Study on array of photo-detector based absolute rotary encoder

“…According to the placement of code scale and sensing head in an encoder housing, it is classified as reflection and transmission type. A reflection type encoder is designed by Hak-Soon and Sang-Shin [10] where a beam router transmits a light beam and reflects back to the sensing detector from a code scale. Thus during the displacement of code scale according to the object, coding information is translated into modulated electric signal (sinusoidal waveform, phase difference of 90 • ) by two semicircular silicon PDs.…”

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

“…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.…”

“…There are continual contributions to the field of optical encoders based on achieving improvements in one of the following key aspects: resolution, stability, size, and cost. For example, in some of the more recent referenced papers, the emphasis is on the size and cost through a design using embedded gratings and a passive alignment system [14] and through clever integration of the structured light source and the four photodetectors with their masks on a monolithic Si substrate [15].…”