Diffractive incremental and absolute coding principle for optical rotary sensors

We are presenting a new optical encoder architecture for shaft encoding, both in incremental and absolute modes. This encoder is based on a diffractive optics technology platform. We have developed various disk based rotary diffractive encoders previously. This encoder is different in the way it is not a disk composed of successive gratings or computer generated holograms, but rather composed of a single element placed on the shaft. It is thus best suited for hollow shaft or end of shaft applications such as in encoder controlled electrical motors. This new architecture aims at solving some of the problems encountered with previous implementations of diffractive encoders such as disk wobble, disk to shaft centering and also encoding in harsh environments.

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“…There are at least two different ways to implement diffractive encoders, either implemented as rotary disks or linear strips [3], [4] and [5].…”

Section: Diffractive Encodersmentioning

confidence: 99%

Novel optical encoder for harsh environments

Kress

Muêller²,

Brac-de-la-Perriere

2014

SPIE Proceedings

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“…Linear encoder as an important displacement measurement device has been widely used in manufacturing industry [1,2]. The reading methods of a typical linear encoder can be divided into incremental method based on the theory of the Moiré phenomenon and absolute method [3,4]. Moiré fringe is generated when an index scale superposed on a main scale [5].…”

Section: Introductionmentioning

confidence: 99%

Analysis of Signal Distortion Caused by Opening Ratio Variation of Main Scale and Index Scale in Linear Encoder

Yin

Shi

et al. 2013

AMR

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Linear encoder as an important displacement measurement device has been widely used in manufacturing industry. The accuracy of linear encoder is based on the precision of its scales. In this article, the manufacturing process of the scales based on photolithography process and etching process was discussed in order to explain the opening ratio variation. A mathematical model was derived to analyze the effects of opening ratio variation on the waveform of output signal. The result shows that the waveform of the signal is cut off in comparison with the ideal waveform, and the magnitude of the output signal is changed.

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Laser direct writing

Häfner

Pruß

2011

Optik & Photonik

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Diffractive optics are compact and flexible optical elements with attractive properties that conventional refractive or reflective surfaces cannot deliver. While their fabrication is still challenging, the developments over the past years in both replication and mastering have advanced their application in fields like illumination shaping, metrology, laser beam forming, polarization shaping or fraud protection. A powerful tool for mastering is the technology of laser direct writing, initially developed for applications like mask production for lithography or mastering for optical data storage. In this contribution we present recent developments in laser direct writing technology for diffractive optics.The efficient fabrication of diffractive optics is of growing interest for many applications. While in conventional systems refraction or reflection on smooth optical surfaces is used to redirect the impinging light, a diffractive optical element uses diffraction on a microstructured surface to shape the incoming light into the desired output light field. The shape and position of the microstructures define their functionality. Typical structure heights for diffractive structures used in the visible spectrum are in the micrometer range, while the lateral dimensions of the individual microstructures can range from the order of the design wavelength or below up to several millimeters. Typical structure shapes are binary elements with only two levels in the structures, multilevel elements or quasi-continuous, saw-tooth like structures. Laser direct writingLaser direct writing of such structures has proven to be a flexible, fast and cost-effective approach. Depending on the application and process, the fabricated structures are used directly in the application or form the master shape for a subsequent replication process. Figure 1 gives a principle overview. There are processes that use laser direct writing to directly structure the surface (e.g., via ablation or thermal processes) or modify optical properties like the refractive index to obtain a diffractive optical element directly, but more common are photoresist based processes known from lithography as used in semiconductor manufacturing. Here, a photo sensitive layer, the photoresist layer, is coated onto a substrate. The thickness of the layer depends on the required structure depth and the subsequent process; typical values are a few hundred nanometers to a few micrometers. The photoresist changes its solubility depending on the energy that is absorbed by the writing laser. This allows in the subsequent developing step to obtain a photoresist profile from the light pattern that was written into the layer. The photoresist profile can be used directly as diffractive element for wavelengths

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Diffractive incremental and absolute coding principle for optical rotary sensors

Cited by 12 publications

References 5 publications

Novel optical encoder for harsh environments

Novel optical encoder for harsh environments

Analysis of Signal Distortion Caused by Opening Ratio Variation of Main Scale and Index Scale in Linear Encoder

Laser direct writing

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