JP2011099869A - Optical encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems wherein, when loading an optical encoder in a small space of a lens barrel or the like, a transmission type constitution which is unsuitable for miniaturization requires a large number of components and has poor work efficiency for assembly, and although a constitution for detecting a cylindrical scale by a reflection sensor is preferable, a scale curvature problem makes highly accurate detection difficult, and a method for improving an illumination system of the sensor is unsuitable for miniaturization, because a sensor size becomes large. <P>SOLUTION: In this encoder, a reflection type scale having a cylindrical shape is irradiated with a point light source, and a pitch of the reflection scale is set at a proper value so that a pitch of an interference fringe formed by reflected diffracted light flux from the reflection scale agrees with a light receiving element pitch on a desired gap setting position. A detection sensor and the scale therefor are also provided. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a displacement detection device that detects displacement of a moving body, and more particularly to an angle detection device that optically detects an angle. For example, an interchangeable lens for a single-lens reflex camera, a digital video, and a lens mounted on a digital camera The present invention relates to a displacement detection mechanism suitable for a lens barrel and the like.

  Conventionally, an encoder is used as an interchangeable lens for a single-lens reflex camera, a lens position detection unit of an autofocus mechanism mounted on a video camera or a digital camera, or a manual operation unit, for example, a displacement detection mechanism for detecting a rotational displacement of a manual ring. (For example, refer to Patent Document 1).

  FIG. 17 is a diagram showing a configuration of main parts of a rotary encoder mounted on an interchangeable lens for a single-lens reflex camera. In FIG. 17A, the center line Z is the lens optical axis of the interchangeable lens.

  The main scale 620 is indirectly connected to a lens straight drive cam (not shown), and has a structure in which the straight position of the lens can be detected by detecting the rotation angle of the main scale 620.

  FIG. 17B is an enlarged view of the main part V of FIG. An index scale 630 is disposed opposite to the main scale 620, and a rotation angle of the main scale 620 is detected by a photo interrupter including a light emitting element 601 and a light receiving element 604 disposed so as to sandwich the two scales.

  As another conventional example, there is one that attempts to detect a rotation angle by providing a reflection scale on a cylindrical body. A sensor is arranged outside a cylindrical body (for example, see Patent Document 1). Or there exists what has arrange | positioned the detection sensor inside the cylindrical body (for example, refer patent document 2).

  Hereinafter, they will be described with reference to FIGS.

  In FIG. 18A, a lattice pattern 702 composed of a strong reflection portion 702a having a high light reflectivity and a weak reflection portion 702b having a low reflectivity is continuously formed on the surface of a rotating body 701 whose rotation change amount is to be measured. Is formed. The lattice pattern 702 is provided by directly printing a pattern on the rotating body 701 or by adhering a thin film member on which the pattern is formed to the rotating body 701. FIG. 18B shows an example in which a detection sensor is arranged inside a cylindrical body. A detection unit including a light source 715, a light receiving unit 716, and an index scale 713 are arranged inside the cylinder.

  In addition, there is an apparatus in which a sensor is arranged outside a cylinder and an attempt is made to improve the detection optical system for the purpose of high-precision detection (for example, see Patent Document 3).

  The configuration will be described below with reference to FIG. In FIG. 19, separate optical configurations are arranged in one drawing in the right half and the left half, and two optical configurations are shown.

  First, the configuration of the left half will be described. The light beam emitted from the light source L2 is collimated by the collimator lens K and passes through the flat fixed grating AT2. Then, after being reflected by the cylindrical grating WT2, it passes through the fixed grating AT2 again and is reflected on the photoelectric element P2 (not shown).

  Since the surface M2 of the cylindrical lattice support T2 is curved, among the light rays parallel to the optical axis OA2, the light rays on both sides of the optical axis OA2 are on the surface of the cylindrical lattice WT2 in the drawing plane. Incident in a state not perpendicular to. Thereafter, the light is reflected in the drawing plane and reflected outside the effective area on the fixed grating AT2.

  On the other hand, in the configuration of the right half of FIG. 19, the collimator lens K is set so that the light beam is directed to the center B2 of the cylindrical grid support T2, so that the radial direction is relative to the rotation axis D2 of the cylindrical grid support T2. Since the light beam is directed to the outside, the light beam is not reflected outside the effective area.

  In contrast to the case where the cylindrical grating WT2 is illuminated with a parallel light beam as in the configuration on the left side, the collimator lens K is used so that the illumination light beam is directed toward the center of the cylindrical body in the configuration on the right side. Light rays are incident at the right position.

  In the configuration example on the right side, the grating pitch of the fixed grating AT2 is set to a ratio of R2 + a2 with respect to the grating constant R2 of the cylindrical grating WT2 for the rays in the radial direction. Here, a2 represents the gap between the cylindrical lattice WT2 and the fixed lattice AT2.

  In this conventional example, the illumination means from the light source is improved (right side configuration) so that the light beam is irradiated perpendicularly to the curved surface of the cylinder and the light beam is optimized to return to a desired reflection position. Also in the fixed grating, the fixed grating pitch is set in consideration of the difference in the reading radial position of the pitch on the fixed grating side with respect to the cylindrical grating pitch.

Japanese Patent No. 270401 JP-A-5-203465 JP 59-061711 A Japanese Patent No. 2610680

  In recent years, position detection sensors mounted on interchangeable lenses for digital single-lens reflex cameras, lens barrels mounted on digital video and digital cameras, etc., have been required to have high resolution and high accuracy on the order of micron, and have been miniaturized. There is a strong demand.

  In such a background, since the conventional configuration of FIG. 17 is a configuration of a transmissive encoder, the U-shaped holder member that supports the light emitting element and the light receiving element and the two scales are sandwiched between the lenses. The size in the direction of the optical axis is increased, which is not suitable for downsizing. In addition, the number of parts was large and the assembly workability was poor.

  A configuration in which a reflective scale is attached to a columnar or cylindrical body and detected by a reflective sensor is preferable, as in the conventional configuration of FIGS.

  However, the necessary resolution cannot be obtained with a general-purpose reflection sensor.

  In addition, since they are designed on the assumption of a flat reflection scale, no consideration is given to the light amount loss due to the shake of the light beam due to the influence of the curved surface of the reflection surface, the detection pitch deviation, the sensitivity of the gap characteristics, and the like. Therefore, an output signal characteristic error occurs due to the radius of curvature, and desired performance cannot be obtained.

  In particular, it was practically impossible to use for position detection with high accuracy and high resolution.

  Recent lens systems require submicron position detection resolution.

  In order to detect the cylindrical grating with the reflection sensor, naturally, a detection sensor in consideration of the influence of the curvature of the scale reflection surface is necessary. The prior art shown in FIG. 19 aims to avoid such an error due to the curvature of the scale reflecting surface. By changing the illumination means of the detection sensor from parallel illumination to convergent illumination, high-accuracy position detection is possible without loss of light quantity.

  However, in order to obtain a convergent illumination system, the conjugate length of the lens K increases, and the thickness of the detection sensor (the distance from the radial dimension light source L2 to the cylindrical grating surface M2) increases. Therefore, it is not so large as to be mounted on the desired lens system.

  The object of the present invention is to eliminate the above-mentioned problems and to enable the detection with a small size, high accuracy, and high resolution in consideration of the curvature radius of the curved reflection scale having a constant curvature radius such as a cylinder or a cylinder. Another object of the present invention is to provide an optical encoder applicable to a conventional scale having a planar shape.

In order to solve the above-described problems from the above points, the optical encoder according to claim 1 includes a reflective scale having a grating-like pattern acting as a diffraction grating formed on a curved surface and rotatable about a rotation axis. In an optical encoder having a light source for illuminating the reflective scale with a divergent light beam and a plurality of light receiving elements for receiving the light beam reflected by the reflective scale,
With respect to the reflective scale, the rotational axis of the reflective scale is located on the same side as the light source and the light receiving element.

  As described above, in the present invention, a cylindrical reflective scale is irradiated with a point light source, and the pitch of interference fringes formed by the reflected diffracted light beam from the reflective scale matches the light receiving element pitch at a desired gap setting position. The pitch of the reflection scale was set to an appropriate value. As a result, a signal with high accuracy and high resolution can be obtained.

  In particular, since a divergent light beam from a light source is directly applied to the reflection scale as a detection sensor, a lens is unnecessary and an extremely thin sensor can be obtained.

  In addition, the detection resolution can be changed by appropriately selecting and setting the pitch of the reflection scale and the setting gap according to the relational expression without changing the detection sensor as a feature that could not be obtained in combination with the conventional flat reflection scale. It becomes possible.

  Although only a single resolution can be obtained with the flat reflection scale, the resolution can be selected within a range that is combined with the curved reflection scale.

  Further, when the detection sensor is arranged inside the cylindrical reflection scale, there is an effect of improving the light utilization efficiency as a result of wavefront conversion, and the configuration can be selected according to the purpose.

  A cylindrical lattice can be realized at low cost by using a flexible member such as a film as a means of the cylindrical reflection scale.

  In particular, when a light beam is guided to the light receiving element with high efficiency, a semiconductor laser with good directivity is used as the light source means, so that high-resolution detection is possible with the external winding type.

The perspective view for demonstrating the 1st Example of this invention The figure for demonstrating the structure of a detection sensor Diagram for explaining cylindrical film reflection scale Optical system layout for the flat reflection scale Diagram of equivalent optical system for explaining interference image with divergent beam The figure for demonstrating the optical arrangement | positioning of this invention The enlarged view for demonstrating the optical arrangement | positioning of this invention Schematic ray path diagram Diagram of equivalent optical system with curved reflection scale in the present invention The figure for demonstrating the 2nd Example of this invention The enlarged view for demonstrating the optical arrangement | positioning of this invention Enlarged view for explaining variations of the optical arrangement of the present invention Explanatory drawing of the third embodiment Explanatory drawing of 4th Example Explanatory drawing of 4th Example Expansion of main part of conventional configuration Explanatory drawing of 4th Example Expansion of the principal part of a structure of this invention Illustration of prior art Illustration of prior art Illustration of prior art

  The present invention will be described in detail based on the embodiment shown in FIGS.

  FIG. 1 is a perspective view showing the configuration of a first embodiment of an optical reflective encoder according to the present invention. The reflection scale 20 is bonded and fixed to the inner side surface of the ring-shaped scale support 21 with a double-sided tape. A detection head 40 is disposed inside the scale support 21 so as to face the reflective scale 21. The detection head 40 is composed mainly of a semiconductor element of a light receiving element 30 composed of a light source 10 composed of an LED chip, a photo IC chip incorporating a light receiving section and a signal processing circuit.

  First, the LED chip and the photo IC chip will be described.

  2A to 2C are views for explaining the details of the detection head 40 of the present invention.

  FIG. 2A shows details of the LED chip and the photo IC chip. The LED chip 10 is a point light emitting LED having a current confinement structure, and the effective light emitting region 11 has a circular light emitting window having a diameter of about 70 μm. The emission wavelength is a red LED of 650 nm. The photo IC chip 30 is disposed below the LED chip (A). The photo IC chip 30 includes a light receiving element portion 31 and a signal processing circuit portion on the side close to the LED 10. In the light receiving element portion 31, 16 photodiodes are arranged at equal intervals in the horizontal direction of the figure, and are 32a, 32b, 32d, 32d,... 35a, 35b, 35c, 35d in order from the left.

  In the first embodiment, the fundamental spatial frequency component of 256 μm is arranged to be detected as the intensity distribution of the light projected on the light receiving element surface. This period is called the basic detection period of the head, and is represented by the symbol P hereinafter. The 16 light receiving elements are arranged at a P / 4 pitch (in this case, 64 μm) with respect to the detection basic period P, and thereby two photos that obtain outputs of A and B phases that are 90 ° out of phase. A plurality of sets of four photodiodes each including a diode and two photodiodes that obtain outputs of AB and BB phases that are 180 ° out of phase with each other are arranged. In this embodiment, there are four sets of 32, 33, 34, and 35.

  That is, as the scale is moved, A, AB, B, and BB phase output currents that are shifted in phase by 90 ° are obtained. These currents are converted into voltage values by a current-voltage converter, and then each of the A phase is output by a differential amplifier. A and B phase displacement output signals having a 90 ° phase shift are obtained by taking the differential between A and B phases and the differential between B and BB phases.

  2B and 2C are diagrams illustrating a package for sealing the semiconductor element. FIG. 2B shows a light shielding wall 48 disposed so that light does not enter the light receiving element 31 directly from the light emitting region 11 of the light source 10. FIG. 2C shows a cross section of a detection head and a reflection scale and a simple light beam path. In addition to the light source 10 and the light receiving element 30, the detection head 40 is disposed on the wiring substrate 44, a light-transmitting sealing resin 45 sealed so as to cover the light source 10 and the light receiving element 30, and the sealing resin 45. It consists of a transparent glass 46 provided.

  Next, the reflection scale will be described with reference to FIG. In this embodiment, as shown in FIG. 3A, the planar reflection scale of FIG. 3B is fixed to the inner surface of the ring-shaped support 21 with a double-sided tape (not shown). The reflective scale may be formed directly on the inner surface of the cylinder by other means.

  As shown in FIG. 3C, the reflective film scale 20 includes a pattern forming sheet 23 and a reflective layer forming portion sheet 24. The pattern forming sheet 23 is, for example, a transparent PET film for industrial photoengraving film, has a thickness of about 0.1 to 0.2 mm, and is subjected to an exposure / development step by an emulsion layer of the industrial photoengraving film. Necessary patterns are formed. On the base material portion 23a of the pattern forming sheet 23, a pattern composed of a non-reflecting portion 23b and a light transmitting portion 23c of a light absorbing portion is alternately provided.

  On the other hand, in the reflection layer forming sheet 24, a reflection layer 24b made of a vapor deposition film is formed on the lower surface of the reflection layer 24a made of a PET film as a base material. The reflective scale 22 has a structure in which the pattern forming sheet 23 and the reflective layer forming sheet 24 are joined by an adhesive layer 25 made of a transparent adhesive as shown in FIG.

  Such a reflective scale 22 has flexibility with a thickness of about 0.2 mm, and a long flat reflective linear scale (B) is formed on the inner surface of the cylinder as shown in FIG. It is possible to wear it curved.

[For flat reflection scale]
Next, in describing the optical characteristics of the curved reflection scale according to the present invention, the principle for detecting a planar reflection scale with the detection sensor of the present invention will be described.

  The optical action when a flat reflection scale is irradiated with a divergent light beam is considered in FIG. FIG. 4 is a configuration diagram of a reflective encoder. Here, the reflection scale 20 is treated as a reflection scale on a flat plate. The flat reflection scale 20 is irradiated with a divergent light beam from the light source 10, and interference fringes are formed on the light receiving element 31 of the photo IC chip 30 by the reflected diffracted light from the reflection scale 20. The light receiving element 31 and the reflection scale 20 are arranged with a gap G. In this configuration, if the pitch of the reflection scale 20 is Ps, interference fringes (period P) corresponding to a period twice the pitch Ps of the reflection scale 20 are formed on the light receiving element surface.

  This will be described with reference to FIG. 5 showing an equivalent optical system having the configuration shown in FIG. In FIG. 5, the movement axis of the central reflection scale 20 is X0, the surface of the light receiving element 31 is X2, and the light source 10 is arranged on the X1 axis. The light emitting point 11 of the light source 10 is arranged at the coordinate L0. The gap G between the reflection scale 20 and the light receiving element 31 shown in FIG. 5 corresponds to the distance (G) between X0-X2 and X0-X1 in FIG. A ray diagram in which a divergent light beam is irradiated from the position of the light source coordinate L0 onto the reflection scale 20 arranged on the X0 axis and the light ray is diffracted on the diffraction grating surface is drawn. The light reaching the origin (0, 0) on the reflection scale surface from L0 is diffracted at the diffraction angle θ1 and reaches the light receiving element 31. When the direction of the diffracted light beam is extended in the direction opposite to the traveling direction of the light beam, and the point where the origin intersects with a circle of radius G having (0.0) as L is L + 1, the diffracted light beam has a light source arranged at L + 1. A wavefront similar to the light wave formed is formed.

  Therefore, the diffracted light beams of the respective orders are arranged on the circumference on the radius G according to the diffraction orders as in such virtual light source points L + 1, L-1,. The light intensity distribution of the interference image can be calculated as superposition.

  From this relationship, the intensity distribution of the interference fringes projected on the light receiving element surface indicates that an interference fringe (period P) corresponding to a period twice the pitch Ps of the reflection scale 20 is formed.

  Next, consider the case of a curved reflection scale, which is the subject of the present invention.

  FIG. 6 is a diagram in which the cylindrical support 21 and the main components in the detection head are omitted, and the reflection scale 20, the light source 10, and the photo IC 30 fixed in a cylindrical shape are laid out in the configuration of this embodiment. In the figure, the center of the cylindrical reflection scale 20 is set to the rotation angle detection axis Y0 axis, and the rotational displacement of the reflection scale with the Y0 axis as the rotation axis is detected by a detection head 40 (not shown). Here, let R be the distance (= radius) between the reflection surface of the cylindrical reflection scale and its center. FIG. 7 is an enlarged view of a main part of FIG. The relationship regarding the arrangement of the light source 10, the light receiving element 30, and the reflection scale 20 will be described with reference to FIG.

  First, when the coordinate system is determined, the coordinate system having the origin (0, 0, 0) at the center of the light emitting region 11 of the light source 10 is (x1, y1, z1), and the cylindrical reflection scale shown in FIG. The axis connecting the 20 central axis Y0 and the light emission center of the light source (= the origin of the coordinate system) is z1, and the axis parallel to the rotation axis Y0 is y1. The tangential direction for rotational displacement detection is the x1 axis. Moreover, the lattice strip of the reflective scale 20 is formed in parallel with the rotation axis Y0. The distance from the light emitting surface of the light source 10 to the substantial reflecting surface position (= the distance R from the central axis Y0) of the reflecting scale 20 is called a gap and is represented by G. Then, eight of the 16 light receiving elements are arranged on the target about the y1 axis. The center coordinates of the light receiving element are expressed as (0, −Ds, 0), where Ds is the distance between the centers of the light emitting element and the light receiving element.

  The reflection position coordinates on the reflection scale 20 are (x, y, G).

  Considering the case where the reflection scale having the relationship of pitch Ps = 1 / 2P is fixed in a cylindrical shape in the above positional relationship, the divergent light beam emitted from the light emitting region 11 of the light source 10 remains the divergent wave surface. The light enters the reflection scale 20 and part of the reflected wave reaches the light receiving element 30. Unlike the planar reflection scale shown in FIG. 4, the reflection scale has a cylindrical concave shape. Therefore, when a 1/2 pitch scale of the light receiving element pitch P is used as the curved reflection scale, the period is longer than the light receiving element pitch P. A small interference fringe is formed on the light receiving surface. Specifically, in this embodiment, the detection basic period P of the light receiving element is 256 μm, and a reflection scale of 128 μm, which is an appropriate pitch when using this detection head and the flat plate reflection scale 20 in this way, is used. When the shape is fixed to a cylindrical shape and used as shown in FIG. 1, the light receiving element surface has a light intensity distribution with a period smaller than a period of 256 μm.

  FIG. 8 is a view of the cylindrical scale as viewed from the axis Y0 representing only the semicircular portion. In this figure, the pitch Ps of the reflection scale is changed so that the light beam from the light source is reflected at the pitch P on the light receiving element, so that the pitch of the interference fringes is forcibly adjusted. Although it is impossible to make the pitch uniform on the light receiving element surface, it has been confirmed that a characteristic that is practically sufficient can be obtained by adjusting the average pitch size on the light receiving surface.

  The change in the basic period of the interference fringes is considered in the same manner as in the equivalent optical system with the divergent light beam in FIG.

  Due to the reflection at the curved surface, the divergent light beam from the light source has undergone a wavefront change. In this case, since the spread of the divergence wavefront is suppressed by the influence of the concave cylindrical surface, each diffracted light beam from the reflection scale 20 to the light receiving surface is obtained as a result of wavefront conversion as shown in the equivalent optical system in FIG. It can be considered that the wavefront has moved from the position of the virtual light source points L0, L +, L− in FIG. 5 to the position of Z ′ in the figure. As a result, although the distance Z from the reflection scale diffractive surface to the light receiving element does not change, the light source positions of the virtual light source points L0, L +, L−, etc. become Z ′, and it can be interpreted that the formation pitch of the interference image has changed. In the case of a flat surface, the distance between the light source point and the reflection scale and the reflection scale and the light receiving surface are equal. As a result, there is a relationship of 2 × Ps = P between the reflection scale 20 pitch Ps and the interference fringe pitch P. It was. That is, in the figure, when (Z + Z) / Z is a plane, the magnification is (Z ′ + Z) / Z ′ in the present embodiment, and the interference fringe magnification does not become twice the reflection scale pitch. In addition, when the wavefront conversion is reversed, that is, when the cylindrical surface is convex, this corresponds to the case where a reflection scale is provided on the outer side surface of the cylindrical reflection scale and the detection head 40 is disposed opposite to the scale reflection surface. At that time, it can be seen that the virtual light source point moves to the position Z ″ in FIG. 9 and the magnification is larger than two times.

  Now, let us consider the derivation of the reflection scale pitch correction value when the sensor having the detection basic period P of the detection sensor is applied to the configuration in which the detection head 40 is disposed inside the cylindrical scale 20.

  There are various approaches as a calculation method for obtaining a desired interference fringe pitch on the light receiving surface. Here, the optical path length L1 of the light source 10 and the reflection scale 20 and the reflection scale are used by using the principle of the shortest optical path (Fermat's principle). 20 and a coordinate point (x, y, G) on the reflection scale surface where the sum of the optical path lengths at the center of the light receiving element 31 (the following formula f (x, y)) is minimized, and the cylindrical scale is obtained from the x coordinate value. The scale pitch to be attached to the can be determined.

However,
Radius of cylindrical reflection scale: R
Distance between light source and reflection scale: G
Distance between light emission center and light reception center: Ds
Basic detection pitch of detection head: P

  The correction pitch calculated in this case is established in the vicinity of the optical axis, but a pitch shift occurs in a distant portion. Therefore, it is necessary to determine the correction pitch in consideration of the number of light receiving element elements so that the average pitch is matched in the entire light receiving element. .

  As described above, in the case where a cylindrical reflection scale is used, the gap surface radius G is set in consideration of the reflection surface radius of curvature R, and the basic detection pitch of the detection head (= light receiving element). The optimum reflection scale pitch can be determined from the interference fringe pitch P) and the distance Ds between the light source and the light receiving element, thereby enabling highly accurate position detection similar to a flat plate reflection scale despite being cylindrical. is there.

  Here, the configuration of the first embodiment is referred to as an “inner winding type”.

In the second embodiment, the relationship between the gap value G and the radius R of the cylindrical reflection scale 20 in this inner winding type will be described. FIG. 12 shows the state of the optical path for seven cases of the inner winding type, and expresses the degree of the pitch of the reflection scale.
(A) shows a case where the gap is relatively small, and (B) shows a case where G = R / 2. In this case, the pitch Ps of the reflection scale is equal to the detection basic period P of the detection head = the light receiving element pitch.
The relationship is (Ps = P). In (C), the pitch of the reflection scale must be increased, and the resolution as a rotary encoder is low, so it is not very valuable.
In (D), the light beam is condensed on a part of the light receiving surface, and no stripes are formed. In the state (E), the moving direction of the fringe changes, and as a result, the AB phase signal phase is inverted. Inversion of the moving direction of the stripe occurs at a pitch substantially equal to (F) and (A).

  As already described in the first embodiment, the case where the reflection scale is provided on the outer surface of the cylinder as the cylindrical reflection scale and the detection head 40 is disposed opposite to the scale reflection surface will be described.

  10 and 11 are diagrams for explaining an embodiment in which a reflection scale is provided on the outer surface of the cylinder and the detection head 40 is disposed opposite to the scale reflection surface.

  Since the difference between the detection sensor 40 being inside or outside the cylindrical scale is the same as in the first embodiment, the detailed description thereof is omitted. Here, this configuration is referred to as an “outer winding type”, and the configuration of the first embodiment is referred to as an “inner winding type”.

  Although the feature of the external winding type has already been described in the first embodiment, the pitch Ps of the reflection scale 20 is corrected to a small value, so that the resolution increases when the radius R is considered constant.

  Specifically, as shown in FIG. 13, when the cylindrical scale diameter is considered to be constant, high-resolution rotation detection can be achieved by selecting a pitch correction value with a setting for separating the gap.

  As the gap dimension G increases in the order of (A) to (C) in FIG. 13, the pitch of the reflection scale needs to be reduced, and as a result, the rotation angle detection resolution is improved.

  Usually, the detection sensor can read only a specific detection pitch.

  That is, the fundamental wave spatial frequency of the interference fringes (light intensity distribution having a periodic intensity distribution) projected on the surface of the light receiving element at the light receiving element arrangement pitch is read. Therefore, in order to cope with various resolutions, it is necessary to individually correspond to the arrangement pitch of the light receiving elements.

  In recent years, the light receiving element has been mainly composed of a so-called photo IC chip in which electronic circuits such as an amplifier circuit, a digitizing circuit, and an electric dividing circuit are integrated.

  When considering the correspondence to various resolutions, the number of divisions is arbitrarily changed by electric division. We are trying to cope with this.

  An IC mask cost for manufacturing the photo IC is required, and the assortment of the light receiving element pitch in accordance with the required resolution is not economical.

  In the rotary encoder, the resolution per rotation can be changed by changing the scale diameter of the encoder, and the resolution can be changed by changing the diameter in the same manner in the cylindrical lattice type of this time as well. However, as shown in Examples 2 and 3, according to the present invention, the resolution can be changed without changing the diameter of the cylindrical lattice.

  When the sensor is arranged inside the cylinder as in the second embodiment, it can be made coarser than the pitch read at the time of the plane scale.

  As in the third embodiment, when it is arranged outside, it is possible to achieve high resolution.

  As an example, a cylindrical scale with a cylindrical lattice diameter of φ10 mm can be made to have a resolution of 4 times or more. In this case, however, a gap needs to be widened, and a semiconductor laser in which energy is concentrated near the chief ray even with a divergent light beam (Surface emitting laser) is an effective light source.

(Camera mounting example Optical axis direction dimension reduction example)
An embodiment in which a sensor and a scale according to the present invention are mounted on a lens barrel will be described below with reference to the drawings.

  14 is a sectional view of a conventional lens barrel, FIG. 15 is a sectional view of a driving force generating unit 35 incorporated in the lens barrel of FIG. 14, and FIG. 16 is incorporated with the sensor and scale of the present invention. 4 is a cross-sectional view of a unit 35. FIG.

  14, 15, and 16, reference numeral 501 denotes an outer cylinder of the lens barrel, 502 denotes a fixed cylinder that is disposed inside the outer cylinder 501 and is screwed to the mount, and 503 and 504 denote the driving force generation unit 535. It is a fixed cylinder that is a frame or a base plate. The fixed cylinder 504 is screw-fixed to the fixed cylinder 503, and the fixed cylinder 503 is screw-fixed to the fixed cylinder 502.

  505 has an outer cylinder portion 505 a disposed in front of the outer cylinder 501, a fixed cylinder 503, and an inner cylinder portion 505 b disposed inside the fixed cylinder 504.

  A fixed cylinder 503, a fixed cylinder fixed to the fixed cylinder 504 with screws, 506 are circumferential grooves formed on the outer peripheral surface of the outer cylinder portion 505 a of the fixed cylinder 505 and circumferential grooves formed on the outer peripheral surface of the outer cylinder 501. It is fitted and can be rotated around the center axis of the lens (ie, the optical axis Z).

  In addition, the manual operation ring supported so as to be movable in the optical axis direction provides a click feeling when moving in the optical axis direction by the claw portion 501a of the outer cylinder 501 and the groove portion 506b provided in the inner peripheral portion of the manual operation ring 506. At the same time, it is held at each position after being moved in the optical axis direction.

  On the outer peripheral surface of the fixed cylinder 503, as shown in FIG. 15, all the components (512 to 520) of the vibration wave motor 533, the rotary cylinder 520 that rotates integrally with the rotor 518 of the vibration wave motor 533, and the rotation A motor bearing / output member 534 that contacts the cylinder 520 and a manual operation force input ring 523 for inputting the rotational torque of the manual operation ring 506 are mounted.

  A main scale (hereinafter referred to as a pulse plate) 524 of a conventional optical encoder is coupled to an output member 534 (hereinafter referred to as a coro ring. In the figure, hatched parts are shown).

  In FIG. 15, 525 is an interrupter that outputs a signal corresponding to the angular position of the pulse plate 524 to the LENS CPU. Reference numeral 530 denotes a lens holder driving key fixed to the ring 522 with a screw.

  The drive key 530 is incorporated through a hole 503a penetrating the fixed cylinder 503, and a roller 529 (not shown) fixed to the lens holder 532 is fitted into a groove 530a provided in the drive key 530. .

  Next, the operation of the lens barrel of the present embodiment having the above structure will be described.

  First, when the user of the lens barrel tries to drive the lens holder 532 with the force of the vibration wave motor 533, the focusing switch (not shown) is operated (autofocus) or the manual operation ring 506 is operated. Rotate.

  When the focusing switch is operated, the control circuit (not shown) is operated to apply a voltage to the electrostrictive element 515.

  As a result, vibration that travels in the circumferential direction occurs in the stator 516, and the rotor 518, the rubber ring 519, and the rotating cylinder 520 are rotated about the optical axis Z by the vibration of the stator 516.

  By these rotations, the hollow roller 521 receives rotational torque from the rotating cylinder 520. However, the manual operation force input ring 523 does not rotate due to friction with the friction ring 526. Accordingly, the roller 521 rolls along the end surface of the manual operation force input ring 523 while rotating around the roller support shaft 522a.

  Since the ring 522 is rotated around the optical axis Z via the roller support shaft 522a, the lens holder 532 is rotated along the cam 505a while being rotated about the optical axis Z by the lens holder driving key 530. Auto focusing is performed by moving in the optical axis direction.

  The structure of a conventional transmissive encoder will be described in the encircled portion VE in FIG. The photo interrupter 525 and the pulse plate 524 are configured as shown in the figure, and the rotation angle of the pulse plate 524 is detected.

  The U-shaped photo interrupter 525 is assembled to the pulse plate 524 so as to be incorporated from the inner surface of the lens barrel, and the workability is not good.

  Further, since the dimension of the photo interrupter 525 in the direction along the optical axis direction Z is large, the degree of freedom in layout is low, and this encoder unit cannot be accommodated in the optical axis direction range of the drive unit 535 in FIG.

  Since there is a space between the fixed cylinder 503 and the rotor member 518, the space shown by the encircled portion VF in the figure, and the encoder portion is provided in this portion, so that the size in the optical axis direction can be greatly reduced. The dimension L shown in FIG. 16 is a reduced dimension.

  FIG. 16 shows that mounting in this region VG (same as region VF in FIG. 15) is possible by the sensor and scale of the present invention.

  The reflection sensor 540 and the reflection scale 541 are arranged as indicated by the enclosed region VG in FIG. A reflective scale 541 made of film is attached to the inner side surface of the roller ring 534 with a double-sided tape. The thickness of this scale is about 0.3 mm.

  On the other hand, the reflection sensor 540 has a part of the fixed cylinder 503 cut out, and the reflection sensor 540 mounted on the flexible substrate is mounted. The thickness of the reflection sensor is about 1.56 mm, and the gap between the reflection scale 541 and the detection sensor 540 is about 0.85 mm. The value obtained by accumulating the thickness dimension (radial dimension) is 0.3 + 1.56 + 0.85 = 2.71 mm, and the total thickness of the sensor mounting portion is within the radial dimension within 5 mm.

  In this example, the basic detection pitch of the detection sensor 540 is 128 μm.

  It is affixed to the inner surface of the roller ring 534 (the diameter φ60.9 of the scale affixing surface on the inner surface).

  Considering the reflection position in the thickness direction of the film reflection scale, the optical thickness dimension of the film, the optical path length of the optical path in the detection sensor, etc., from the light path L1 from the light source to the reflection scale and the reflection scale The f (x, y) coordinates are obtained for the reflection point that takes the minimum value of the sum of the optical paths L2 to the light receiving surface. As a result, the reflection scale pitch Ps was determined.

  Relational expression of the present invention:

  Since the reflection sensor is disposed on the inner surface, the scale pitch is determined to be 134 μm in consideration of the design gap (gap) as a result of the arrangement condition and scale pitch correction according to the present invention.

  In the lens, electrical division (32 divisions) is performed using the analog signal with a period of 134 μm, and a final resolution of 134 / 32≈4.2 μm is obtained.

  The ultra-small reflective detection sensor of the present invention and the reflective scale made of film enable mounting in this small space. The high-precision optical encoder that is the subject of the present invention and that is ultra-compact and that supports high resolution can be realized.

DESCRIPTION OF SYMBOLS 10 Light source 11 Light emission area 20 Reflection scale 21 Ring-shaped cylindrical support body 22 PET base material 23 Photosensitive layer 24 Reflective layer 30 Photo IC
31 Photodetector 32 to 35 Light-receiving element element group 40 Detection head 44 Semiconductor chip mounting substrate 45 Transparent resin 46 Transparent glass 48 Light-shielding wall R Radius of cylindrical reflection scale G Distance between light source emission point and reflection scale reflection surface P within detection head Ps Detected pitch Ps Reflection scale pitch Ds Distance between the center of the light emitting area of the light source and the center of the light receiving area of the light receiving element L0 Virtual light source point of 0th order diffracted light L + Virtual light source point of + 1st order diffracted light L− −1st order diffracted light Virtual light source point 540 detection sensor 541 reflection scale

Claims (1)

A reflective pattern that is formed on a curved surface and functions as a diffraction grating and is rotatable about a rotation axis, a light source for illuminating the reflective scale with a divergent light beam, and reflected by the reflective scale In an optical encoder having a plurality of light receiving elements for receiving a light beam,
An optical encoder, wherein a rotational axis of the reflective scale is located on the same side as the light source and the light receiving element with respect to the reflective scale.

Images