Mitutoyo Corporation

Toshirou Yoshinaka

Tetsuro Kiriyama

Ryuichi Koiso

Two-phase sinusoidal signals QA, QB output from an encoder are interpolated by sample-and-hold (S/H) circuits and A/D conversion (ADC) circuits, and data D is output in accordance with a data request signal RQ from exterior. For this interpolation of encoder output, a direction discrimination up/down counter is arranged near a two-phase square-wave uniform pulse generating circuit, and the data D is latched and output using a signal which is obtained by delaying the data request signal RQ. This can reduce synchronization errors between the data request signal RQ from exterior and the interpolated data, with an improvement in dynamic precision.

Method and circuit for interpolating encoder output

An offset error, an amplitude error, a phase error and a third harmonic component contained in two-phase sinusoidal signals are removed using relatively simple digital computations. An offset error contained in two-phase sinusoidal signals with a phase difference output from an encoder is detected and corrected. Then, an amplitude error contained in the offset-corrected two-phase sinusoidal signals is detected and corrected. Subsequently, a phase error contained in the amplitude-corrected two-phase sinusoidal signals is detected and corrected. Further, a third harmonic distortion contained in the phase-corrected two-phase sinusoidal signals is detected and corrected. Each correction step includes detecting an error from an ideal Lissajous waveform contained in the corrected two-phase sinusoidal signals, and adding the detected error to an accumulatively added last value to yield a new correction coefficient, thereby dynamically updating the correction coefficient.

Encoder output signal correction apparatus and method

A third harmonic distortion corrector is equipped for correcting a third harmonic distortion contained in a two-phase sinusoidal signals with different phases output from an encoder. A third harmonic calculator/detector calculates the amplitude aand the phase &#x3c6;of the third harmonic using Fourier analysis, based on change in radius r of the Lissajous waveform output from a r-&#x3b8; converter. The third harmonic distortion corrector corrects the third harmonic distortion of the two-phase sinusoidal signal ABbased on the amplitude aand the phase &#x3c6;of the third harmonic calculated.

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Kawasaki, Japan

Toshirou Yoshinaka