Mitutoyo Corporation

Emi Kaneko

Joseph Daniel Tobiason

Tatsuya Nagahama

Eric Altendorf

Toru Yaku

Taizo Nakamura

Atsushi Usami

A photoelectric encoder in which light emitted from a light source is modulated by an optical grating and the modulated light is detected by a light receiving element, includes a one-side telecentric optical system which forms an image of the light modulated by the optical grating. The imaging optical system has an aperture through which part of the light modulated by the optical grating is allowed to transmit, the aperture having a size which is required when a cutoff spatial frequency that is a spatial frequency indicating a resolution limit of the imaging optical system due to the light emitted from the light source has a value between a fundamental spatial frequency of the optical grating obtained by a Fourier transformation and a second harmonic of the fundamental spatial frequency.

Photoelectric encoder with optical grating

A method and apparatus for suppressing loss of scale image contrast due to interference effects from optical path length differences, including lens profile aberrations, are provided in a displacement sensing optical encoder that uses a telecentric imaging configuration. According to the invention, the encoder is configured such that the image light that reaches the detector comprises symmetric ray bundles concentrated symmetrically on opposite sides of the optical axis center at the limiting aperture of the telecentric imaging configuration. Central ray bundles, and/or other ray bundles that have an optical path lengths significantly different than the operational symmetric ray bundles are prevented or blocked. As a result destructive interference is prevented and image contrast is improved.

Lens aberration correction in a doubly telecentric displacement sensor

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Kanagawa, Japan

Emi Kaneko