Technical Brief

Development and Validation of an Adaptive Method to Generate High-Resolution Quadrature Encoder Signals

[+] Author and Article Information
Erva Ulu

Graduate Research Assistant
Department of Mechanical Engineering,
Bilkent University,
Ankara 06800, Turkey
e-mail: erva@bilkent.edu.tr

Nurcan Gecer Ulu

Graduate Research Assistant
Department of Mechanical Engineering,
Bilkent University,
Ankara 06800, Turkey
e-mail: ulu@bilkent.edu.tr

Melih Cakmakci

Assistant Professor
Department of Mechanical Engineering,
Bilkent University,
Ankara 06800, Turkey
e-mail: melihc@bilkent.edu.tr

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received September 27, 2012; final manuscript received December 14, 2013; published online February 19, 2014. Assoc. Editor: Srinivasa M. Salapaka.

J. Dyn. Sys., Meas., Control 136(3), 034503 (Feb 19, 2014) (7 pages) Paper No: DS-12-1321; doi: 10.1115/1.4026315 History: Received September 27, 2012; Revised December 14, 2013

This paper presents a new method to increase the measurement resolution of quadrature encoders. The method contains an adaptive signal correction step and a signal interpolation step. Measured encoder signals contain imperfections including amplitude differences, mean offsets, and quadrature phase shift errors. With the proposed method, these errors are first corrected by using recursive least squares (RLS) estimation with exponential forgetting and resetting. Then, the corrected signals are interpolated to higher order sinusoids using a quick access look-up table generated offline. The position information can be obtained with the conversion of these high-order sinusoids to binary pulses and counting the zero crossings. Using the method presented here, a 10 nm measurement resolution is obtained using an encoder with 1 μm off-the-shelf resolution. Validation of the method and the practical limitations are also presented. Further increase in the resolution can be achieved by minimizing the effects of the electrical noise.

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Fig. 2

Measured encoder signals with imperfections

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Fig. 1

General flow diagram of the proposed approach

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Fig. 9

Interpolation results for n = 50

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Fig. 10

Interpolation results for n = 100

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Fig. 11

Validation of the proposed method for (a) n = 100 and (b) n = 50

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Fig. 3

Encoder signal parameters recorded through 120 mm motion of the single axis slider

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Fig. 4

Corrected and measured (actual) encoder signals

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Fig. 8

Single axis slider

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Fig. 5

Interpolation results for n = 25

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Fig. 6

Variation of index number for n = 25

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Fig. 7

Binary pulses obtained for n = 25

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Fig. 12

Tracking performance of the single axis slider



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