Kabushiki Kaisha Okuma Tekkosho

Okuma Corporation

Spectra, Inc.

Keiji Matsui

Atsushi Ieki

Masayuki Nashiki

Yasukazu Hayashi

Kazuhiro Hane

Atushi Ieki

Shuzo Hattori

The amount of the light beam passing through two diffraction gratings is output as an electrical signal by a photo detector. The amount of relative displacement of the diffraction gratings is detected according to the electric signal (output signal) that changes in proportion to the relative displacement. Groove portions and ridge portions are alternately arranged on the first diffraction grating, through which the light beam passes and undergoes wavefront modulation by mutual interference of the zeroth-order diffracted light. This eliminates interference of the zeroth-order diffracted light with a diffracted light of another order, and eliminates changes in the fundamental wave component of the output signal caused by changes in the gap between the two diffraction gratings. The output signal can be made not to include a high-order component by a predetermined modification to at least one of either the array pitch or width of a transparent portion in the second diffraction grating.

Optical encoder diffraction gratings for eliminating diffracted light

The amount of relative in-surface rotation between two scales of a position detector is precisely detected to thereby determine the deviation in longitudinal phase between tracks in one scale. Thus, positional data corresponding to signals from the tracks are made appropriate. The resultant positional data are used so that stable detection of an absolute position is performed. The position detector includes: a first scale provided with a plurality of graduation tracks having different pitches, the first scale being movable in the longitudinal direction thereof; a reading unit having a plurality of detecting sections opposing the graduation tracks, the detecting sections obtaining, from the graduation tracks, signals indicative of a relative movement between the first scale and the reading unit; a conversion circuit for converting the signals obtained by the detecting sections into items of data on positions; and a data processing circuit for combining together said items of said data on said positions so as to obtain data on the absolute position of the first scale, the position detector further including an in-surface rotation amount detecting section for detecting the amount of rotational displacement of the reading unit with respect to the first scale about an axis of rotation constituted by a segment perpendicular to the surface of the first scale, said data processing circuit being adapted to use said rotational displacement amount to appropriately combine together items of data on positions obtained by the conversion circuit so as to obtain data on the absolute position of the first scale.

Position detector

An optical position-detecting apparatus includes an optical block capable of causing interference light having interference fringes perpendicular to a diffraction grating on a subject of measurement to be all the time projected onto the diffraction grating. The apparatus detects the position of a subject of measurement by receiving either light transmitted through a diffraction grating on said subject of measurement or light reflected from said diffraction grating. The apparatus includes an optical block for causing collimated rays generated from a coherent light source to be diffracted, for causing only the '.+-.1' order diffracted light to be extracted and to interfere with each other, and for causing an interference light field area having interference fringes perpendicular to said diffraction grating to be generated and to be projected onto said diffraction grating. Thus, it is possible, with a simple construction, to assure stable outputting of a displacement signal.

Optical position-detecting apparatus

A displacement detecting device generates first and second periodic signals in accordance with a displacement of a relatively movable object. The first and second periodic signals have differing phases relative to each other and each include a third harmonic component and a fifth harmonic component which are approximately equal to each other. The third and fifth harmonic components are equalized by setting a distance between first and second gratings of the position detection device. By equalizing the third and fifth harmonic components of the periodic detection signals, detection errors are reduced.

Position detecting apparatus generating periodic detection signals

A parallel light ray measuring apparatus invention measures the parallelism of a light beam by: receiving a light beam which has passed through two gratings having the same grating period by means of at least two photoelectric converting elements, and by detecting the light intensity obtained from those aforementioned photoelectric converting elements and the phase difference between the periodic signals obtained when either of the gratings is moved, using the at least photoelectric converting elements. Further, the parallel light ray measuring apparatus includes: a first grating; a second grating having the same grating period as that of the first grating, and being disposed such that the grating lines of the second grating are in parallel with those of the first grating; a light pick-up screen for receiving a light beam which has passed through both gratings, whereby the light intensity distribution appearing on the light pick-up screen is detected so as to measure the parallelism of the light beam.

Parallel light ray measuring apparatus

An optical encoder of the present invention includes a first diffraction grating and a second diffraction grating which is displaceable relative to the first diffraction grating to detect the relative displacement. The second diffraction grating has a grating pattern which removes a component having a period which is a factor of 1/n (n: a positive odd number) of the period of a displacement signal representing the relative displacement. In the optical encoder according to the present invention, higher harmonic components are cancelled by adding the amounts of light which passes through the grating portions whose phase differs by a predetermined distance. Consequently, a non-distorted displacement signal can be obtained.

Optical encoder

In an averaged diffraction moire position detector of the present invention, diffracted lights which have passed through the same places as those through which measuring diffracted lights have passed are used for monitoring a quantity of light. Therefore, change in the quantity of light of a light source and change in the transmittance of diffraction gratings can be suitably corrected.

Optical linear encoder with light quantity calabration

A linear encoder has a plurality short main scales arranged separately in their longitudinal direction and plural sliders situated in parallel with the longitudinal direction so as to more along these main scales. In operation, data obtained through these sliders are joined and processed in a signal processor in order to get position data of a table. Consequently, any position along a long movement stroke of the table can be detected easily and at a low cost.

Linear encoder with plural detectors for use with one or more main scales

An averaged diffraction moire position detector has a pair of diffraction gratings. One of the gratings has two grating portions arranged with an offset of half a pitch of the transit portions and the non-transit portions for light. The intensities of light passing through respective grating portions are added to cancel any error component is displacement signals produced when two parts of, for example, a machine tool move. Another averaged diffraction moire position detector uses offset in phase of respective error components contained in the diffracted light of plus and minus of the same number-order. Thus, the intensities of respective diffracted light are added to cancel respective error components, resulting in correct displacement signals being produced.

Optical linear encoder

An optical encoder includes a light source for emitting coherent parallel light and a scale having a grating track for defracting parallel light emitted from the light source. The grating track of the scale includes a plurality of linear adjacent gratings extending in a lengthwise direction. Each of the gratings extends in a widthwise direction direction to define a pitch of the grating. Each grating includes a non-transmitting portion and an adjacent transmitting portion extending in lengthwise direction. The aperture ratio defined by the ratio between a width of the transmitting portion and the pitch of each grating is substantially constant for each of the gratings along the grating track. However, the pitch of each of the gratings of the grating track varies along the grating track. A light spot positioning detector is provided for receiving positive and negative defracted light beams of a same order defracted from a grating track for determining a position of the scale.

Optical encoder with varying grating pitch

In order to detect positions, an optical encoder utilizes the phenomenon that the ratio in intensities of diffracted light beams of different orders change depending on the patterns of aperture ratios in one pitch of a grating on the scale, and that the distance between the positive and the negative diffracted light beams of the same order vary depending on the patterns of the grating pitch on the scale, or that the light spots of the positive and the negative diffracted light beams of the same order move (rotate) depending on the patterns of the grating line direction. Therefore, this optical encoder is free from the adverse influence of fluctuations in the amount of coherent light illuminated from the light source to thereby enable precise positional detection.

High resolution optical encoder having a long detection stroke

In order to detect positions, an optical encoder utilizes the phenomenon that the ratio in intensities of diffracted light beams of different orders change depending on the patterns of aperture ratios in one pitch of a grating on the scale, and that the distance between the positive and the negative diffracted light beam of the same order vary depending on the patterns of the grating pitch on the scale, or that the light spots of the positive and the negative diffracted light beams of the same order move (rotate) depending on the patterns of the grating line direction. Therefore, this optical encoder is free from the adverse influence of fluctuations in the amount of coherent light illuminated from the light source to thereby enable precise positional detection.

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Ooguchi, Japan

Keiji Matsui