Okuma Corporation

Kabushiki Kaisha Okuma Tekkosho

Atsushi Ieki

Keiji Matsui

Masayuki Nashiki

Yasukazu Hayashi

Kazuhiro Hane

Kenji Matsui

An optical encoder, comprising a plurality of light receiving elements 1-12, receiving light that has passed through or been reflected by a scale having a lattice of pitch P, and outputting four-phase signals that have been respectively offset in phase by an integer number of times 90&#xb0; (1/4P). 12 light receiving elements being are in the lateral direction (scale longitudinal direction) with gaps between them of P/60 or 2P/60, four arbitrary light receiving elements arranged next to each other in a row all output signals of different phases, and light receiving elements respectively outputting signals of same phase have three lateral widths of 7OP/60, 13P/60 or 20P/60.

Optical encoder

An encoder has the capability of outputting a stable displacement signal with small distortion. The encoder includes a first scale and a second scale. The first or second scale has a scale pattern in which pattern elements are arranged in such a manner that the spacings between adjacent pattern elements are not constant but vary in phase relative to the reference phase of a reference pattern element by amounts of P/(2.multidot.L), P/(2.multidot.m), P/(2.multidot.n), P/(2.multidot.o), . . . (L, m, n, o, . . . are positive integers, P is the mean pattern period) and by amounts of combinations of sums of these values.

Optical grating and encoder

The optical encoder is capable of detecting phases at positions which coincide more strictly than the phase detecting positions of a conventional optical encoder, and is thereby capable of outputting less distorted displacement signals with a sufficient averaging effect and detecting the phases more accurately. An amount of a light having passed through a first grating is received directly with a light receiving section and output as an electric signal. On the basis of the fact that the electric signal is varied dependently on a relative displacement between the first grating and the light receiving section, the relative displacement is detected. The light receiving section includes a plurality of grating-like photo detecting devices which have fine widths and are arranged in a grating-like shape in a mixed manner within a minute section so as to correspond to four phases. Further, the photo detecting devices are composed of divided and minute photo detecting elements so as to have widths which are not definite but have such values as to eliminate the distorted component of high orders.

Optical encoder for detecting relative displacement based on signals

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

An optical encoder comprising a first scale and photo sensitive elements that shift relative to the first scale along the length of the first scale for determining a relative position based on a plurality of signals having a predetermined phase difference from the photo sensitive elements. The optical encoder comprises groups of photo sensitive elements, wherein each group comprising a plurality of photo sensitive elements arranged side by side in the direction of the length, and wherein each photo sensitive element has a width corresponding to the width of the pattern of the first scale. The groups of photo sensitive elements corresponds respectively to the plurality of signals. The photo sensitive elements belonging to one photo sensitive element group and the photo sensitive elements belonging to the other photo sensitive element group are arranged side by side in a mixed fashion in the direction of the length. One photo sensitive element group and the other photo sensitive element group are arranged so that the signal derived from the one photo sensitive element group and the signal derived from the other photo sensitive element group have a predetermined phase difference therebetween.

Optical encoder used for position detection based upon a plurality of

A scale and encoder are capable of stably outputting a displacement signal with less distortion. The scale has grating pattern lines arranged successively, and the widths of the pattern lines of a second scale are not P/2 but are determined to remove high-order distortion components on the grating pattern. For example, for removing the third and fifth order distortion components, the scale is made to include two slits in which pattern line widths are 17P/30 and 23P/30.

Scale and encoder including differently spaced pattern lines

A position detecting apparatus utilizing optical interferometry changes the wavelength of a light beam from the light source. The variation in the wavelength causes an increment and decrement Cx, Co in the number of waves in the measurement and reference lengths Lx, Lo. The position data calculating section calculates the measurement length Lx on the basis of the detected increment and decrement Cx, Co and the reference length Lo according to an equation, Lx=Lo(Cx/Co). The position detecting apparatus can easily detect an absolute position of an object to be detected.

Position detecting apparatus of optical interferometry

An optical absolute position encoder capable of obtaining absolute position data in a wide range utilizes the fact that the position of a transmitted or reflected light beam is shifted in accordance with the displacement of a grating window and the fact that the grating window can be specified depending upon the characteristics of the light beam which has passed through the grating window. Furthermore, precise position data is obtained by using two gratings which move relatively. The above-described data are combined with each other so that absolute position data revealing high resolution can accurately be obtained for a long stroke.

Absolute position detector with diffraction grating windows and spot

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

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

An optical encoder irradiating light emitted from a light emitting unit includes a rectangular collimator lens having a rectangular face onto a main scale which moves in the longitudinal direction, receives the collimated light beam passing the main scale in a light receiving unit, and optically reads the displacement of the main scale. Since the collimator lens is rectangular, the light emitting unit can be made compact without decreasing the irradiation area of a light beam which is effective in the detection of the displacement. Furthermore, it is possible to increase the irradiation area of the light beam by dividing a collimated light beam from the collimator lens into a plurality of diffracted light beams by a transmitting or reflecting diffracton grating.

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.

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Niwa, Japan

Atsushi Ieki