New ultrahigh-sensitivity absolute, linear, and rotary encoders

UV imprint fabrication of polymeric scales for optical rotary encoders

Optical encoders are mainly used in modern motion servo systems for high-resolution and reliable position and velocity feedback. Pseudorandom optical rotary encoders are single-track and use a serial pseudorandom binary code to measure absolute position. The realization and analysis of such a rotary encoder with advanced code scanning and error detection techniques, as well as an improved redundancy in operation, are presented. A presented serial code reading solution uses two phase-shifted code tracks and two optical encoder modules. So, the realized encoder, hybrid in nature, provides “output on demand” and more or less reliable position information using very efficient error checking. Compared to a standard absolute encoder, this encoder requires a smaller code disc, facilitates installation, has greater flexibility in operation, and is less sensitive to external influences.

Demands for high precision machine tools have been increased as technology advances. Such demands require higher position control to allow the machine tools to produce higher precision end products. To facilitate the position control, magnetic and optical encoders are been widely used in the machine tools. Due to its advantage in withstanding hard environment such as oil, grease and dust over an optical encoder, along with its wide applications in industrial position control, a magnetic encoder has become a desirable choice for machine tools. The objective of this study is to develop a polarity changeable magnetizer for manufacturing coding patterns in a rotary encoder which is used to monitor runout errors for rotating components in machine tools. As opposed to commonly used capacitive pulse magnetizer in which significant amount of energy is required for its electromagnets that potentially causes high energy hazard, in this study, a polarity changeable permanent magnet is proposed and investigated through parameter studies to overcome such issue with the aim placed on producing sufficient magnetization on a thin silicon steel plate to produce desirable coding patterns on the rotary encoders.

To control electro-mechanical engines, high-resolution linear and rotary encoders are needed. Interferometric methods (grating interferometers) promise a resolution of a few nanometers, but have an ambiguity range of some microns. Incremental encoders increase the absolute measurement range by counting the signal periods starting from a defined initial point. In many applications, however, it is not possible to move to this initial point, so that absolute encoders have to be used. Absolute encoders generally have a scale with two or more tracks placed next to each other. Therefore, they use a two-dimensional grating structure to measure a one-dimensional position. We present a new method, which uses a one-dimensional structure to determine the position in one dimension. It is based on a grating with a large grating period up to some millimeters, having the same diffraction efficiency in several predefined diffraction orders (multiple grating). By combining the phase signals of the different diffraction orders, it is possible to establish the position in an absolute range of the grating period with a resolution like incremental grating interferometers. The principal functionality was demonstrated by applying the multiple grating in a heterodyne grating interferometer. The heterodyne frequency was generated by a frequency modulated laser in an unbalanced interferometer. In experimental measurements an absolute range of 8 mm was obtained while achieving a resolution of 10 nm.

WITHDRAWN: Implementation dc motor as servomotor by using arduino and optical rotary encoder

Machine learning-based method for linearization and error compensation of a novel absolute rotary encoder

The development of a multi-turn absolute encoder—a new concept in accordance with a design insensitive to accuracy

This study proposed a rapid prototyping fabrication method for micromotors that allowed us to develop both 1 mm and 1.5 mm diameter permanent-magnet synchronous motors (PMSMs) with an optical rotary encoder. First, an integrated electroforming method was proposed for combining stator housing and flexible print circuit (FPC) coils to ease the manufacturing and assembly of micromotor components. This is particularly useful in the production of prototypes or small volumes of units. Second, an optical encoder was used to detect the rotational angle by means of a reflective code disk, an optical fiber, and a photo-detector. The micromotor was built with a code disk and an optical fiber. The code disk was designed to match the optical fiber and was made by photolithography and sputtering. Both the 1 mm and 1.5 mm diameter motors successfully achieved a rotational speed over 20,000 RPM and due to a 50 µm diameter optical fiber core, the encoders showed a resolution of 12 and 18 pulses per revolution (PPR), respectively.

Subdivision errors and long-period errors are the main components of small absolute optical encoder error. When the external environment changes or the encoder operates for a long time, the subdivision error will increase. In this study, a stepper motor and high-precision encoder are used to develop a system that automatically measures the long-period error and subdivision error of a small optical encoder. The error data are fitted and stored in the program memory of the encoder in the form of an error data table. During the displacement calculation, the encoder collects the peak and valley values of fine-coded two-channel moiré fringe signals in real time, normalizes the moiré fringe signal data, and compensates for the subdivision error and long-period error by looking up data in the table. A 16-bit small encoder was tested using the developed system, and the mean square errors of the encoder before and after compensation were <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$43.3^{\prime \prime }$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$11.7^{\prime \prime }$ </tex-math></inline-formula>, respectively. Therefore, the algorithm proposed herein can significantly improve the measurement accuracy of small optical encoders.

In this paper, a compact absolute optical linear encoder is proposed. The index scale of the proposed encoder has the two track (80 μm and 2 mm pitches), which consist of the pitch-modulated grating and slit-width-modulated grating, respectively. Using the modulated gratings, the harmonic noises of the encoder signals are decreased. Moreover, the respective lines of the slit-width-modulated grating are divided and re-distributed in the index scale to suppress the sensing error due to the contamination on the scale. By fabricating the index scale with silicon photodiode arrays, the proposed advantages are confirmed experimentally.

Electromagnetic encoders exclusively made of a dielectric material are presented in this paper. The proposed encoders consist of a grid (chain) of apertures, which can be arranged circularly (rotary encoders) or linearly (linear encoders) on the considered substrate, a dielectric material. Such encoders can be useful for the measurement of angular or linear displacements and velocities based on pulse counting (similar to optical encoders). Alternatively, the encoder can be used as a near-field chipless-RFID tag based on the presence or absence of apertures at predefined positions in the chain (hence providing an identification code). In both applications, encoder reading is based on the detection of the apertures (pulses) as the encoder moves on top of a dedicated sensing element (reader). In this work, the reader is a microstrip line loaded with a complementary spiral resonator (CSR) etched in the ground plane, and encoder reading is based on the variation of the transmission coefficient caused by encoder motion. Specifically, the notch generated by the CSR shifts up each time an aperture lies on top of the CSR (due to permittivity variation). Thus, the apertures can be detected from the amplitude modulated (AM) signal generated at the output port of the CSR-loaded line, when it is fed by a properly tuned harmonic (interrogation) signal. The main originality of the work is the working principle for encoder reading (permittivity contrast), as well as the lack of metallic elements in the encoder (representing a reduction in fabrication costs).

Use of rotary optical encoder for firing detection in a spark ignition engine

In this paper, a new kind of rotary encoder based on magneto-optical storage method is proposed. By using this method, a rotary encoder with small size, high accuracy and high response can be realized. MO encoder is more advantageous than a magnetic scale and optical encoder according to its high response and its high accuracy, respectively. High accuracy can be achieved by rerecording, therefore the error is corrected. Following issues are described: (1) A device for record, playback and evaluation of accuracy of MO encoder has been developed. (2) A necessary condition for record and playback for MO encoder was experimentally derived. (3) The MO encoder made for trial purposes was recorded by 2250 pulses per revolution directly from the referential encoder, as a result, accuracy of 2.5" and reproducibility of 0.079" were achieved.

Eccentric error is a vital part of high-precision optical encoder error. An automatic error compensation system is designed to lower the eccentric error of the encoder. On the periphery of the fan-shaped code path of the traditional encoder disk, a set of radial code paths is drawn. This radial code path is composed of several concentric circles with alternating light and dark lines. The direction of the radial code path is perpendicular to the direction of the fine code path. When the encoder rotates, the eccentricity of the encoder disk is measured by the moiré fringe signal output from the radial code channel. Based on the eccentricity error compensation algorithm, the eccentricity error of the encoder disk is compensated in real time to enhance the accuracy of the encoder. The experimental results of an encoder show that the mean square error of the encoder before the eccentricity error compensation is 21.25 arc seconds, and it is 3.66 arc seconds after compensation by this algorithm. The algorithm can significantly compensate the error caused by the eccentricity of the encoder and greatly improve the accuracy of the encoder.

This paper proposes a new mathematical algorithm for linear absolute encoder for long distance applications (>100 m). The new algorithm uses a stronger codification method than the classical binary one. Moreover, the proposed implementation uses only four optical sensors which make the method economically efficient. The algorithm and the proposed encoder where tested on an experimental setup. Design of the setup assures the control of all relevant parameters. Experimental results also allow the improvement of the initial algorithm by evolving from binary algebra to the polyvalent algebra (Lukasiewicz- Moisil algebra), using colors coding and color optical sensors.