Patent Application
20140349083
The present application is related to the Japanese Patent Application No. 2013-108899, filed May 23, 2013 and Japanese Patent Application No. 2013-161049, filed Aug. 2, 2013, the entire disclosure of which is expressly incorporated by reference herein.
1. Field of the Invention
The present invention relates to a code plate of an optical encoder.
2. Description of the Related Art
As a code plate of an optical encoder, a code plate disclosed in the Japanese Unexamined Patent Application Publication No. 1999-287671 is known. The code plate of the optical encoder disclosed in this Patent Application Publication includes a reflection portion formed to have a planar surface and a non-reflection portion formed to have a non-planar surface provided alternately in a ring shape. Further, in the non-reflection portion, a V-shaped groove which includes saw-tooth shaped structure or successive mountains and valleys in the cross section is formed.
Now, when it is determined that a direction in which the reflection portion (planar portion) and the non-reflection portion (non-planar portion) are arranged alternatively is referred to as parallel direction, a direction in which multiple V-shaped grooves formed in the non-reflection portion are arranged is the same direction as the parallel direction, further, each V-shaped groove is formed so as to extend toward a radial direction, that is a direction perpendicular to the parallel direction.
Since the V-shaped structures in the non-reflection portion are formed continuously, it may be possible to say that multiple mountains of inverted V-shaped structure are formed. Anyway, since the inclined plane is used to determine the traveling direction of the light flux equally in the both cases, the V-shaped structure and the mountain of the inverted V-shaped structure are referred to simply as V-shaped structure in the following description. Further, it is assumed that a width of one V-shaped mountain or one inverted V-shaped mountain formed by the two inclined surfaces which are continuing mutually is referred to as width.
In order to perform a high-precision encoding, it is expected that the formation period of the reflection portion and the non-reflection portion is made sufficiently fine. When the V-shaped structure is formed, ultimately, it may be conducted that one V-shaped structure is formed in one non-reflection portion and a portion between the V-shaped structures is set to a planar portion. Since the reflection portion and the non-reflection portion are formed alternately at a fine pitch, a high-precision encoding performance can be expected.
Now, a transmission optical rotary encoder is explained. In the transmission optical rotary encoder, when a light flux for detection is irradiated at a predetermined angle, the light flux is transmitted in the planar portion, however, it is reflected totally by the slope of the V-shaped structure in the non-planar portion, accordingly it is non-transparent. In the relation with the light-receiving sensor, in the reflection optical rotary encoder, the light flux is reflected at the planar portion and received, on the other hand, in the transmission optical rotary encoder, the light flux is transmitted at the planar portion and received, further, in the reflection optical rotary encoder, since the light flux is not reflected at the non-planar portion to a predetermined direction, the light flux is not received, on the other hand, in the transmission optical rotary encoder, since the light flux is reflected at the non-planar portion and is not transmitted, the light flux is not received.
When the code plate is formed by the injection molding method, a round R is formed at the top portion of the V-shaped structure that is the convex side of the code plate. Accordingly, in the transmission optical rotary encoder, the light flux for detection is reflected at the non-planar portion, however, cannot be not reflected at the top portion, but is transmitted. Since the light is transmitted, it becomes a cause to reduce the reflectance at the non-planar surface. This reflectance is deteriorated in accordance with the ratio of the width of the top portion for the width of a V-shaped structure. Further, the width of the top portion is mainly determined by the resin mold forming condition.
As described above, thus, in order to achieve a high-precision encoding, a single V-shaped structure may be formed in one non-planar portion, in this case, it is necessary to increase the width of the V-shaped structure to reduce the ratio of the width of the top portion occupying the width of the V-shaped structure, however, since the width of the non-planar portion is determined by the fineness to be required, there is a limit in the reduction of the deterioration of the reflectance.
This patent specification describes a novel code plate of an optical encoder which includes a planar portion that is located on a surface to which a light flux for detection is applied and a non-planar portion that is arranged alternatively with the planar portion on the surface and is comprised of multiple convex structures and concave structures arranged continuously intersecting to a parallel direction of arranging the planar portion and the non-planar portion. The convex structure and the concave structure have a V-shaped structure formed by two planer slopes intersecting each other at a top portion thereof, and when a width of the non-planar portion in the parallel direction is defined as WR, a projected length of the top portion for the surface plane of the code plate is defined as WC, and projected lengths of the two slopes SL1 and SL2 for the surface plane of the code plate are defined as WF1 and WF2, respectively, WC is equal to or more than 2.83 μm, and the following equations (1) and (2) are satisfied:
WF1+WF2+WC>WR (1)
WC/(WF1+WF2+WC)≦0.09 (2)
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
The embodiment according to the present invention is described below referring to the drawings.
A code plate 10 of a transmission optical rotary encoder is formed in a disk shape, on one surface thereof, a pattern structure portion 20 having two ring-shaped concentric circles is formed. In the present embodiment, assuming that the code plate is used in the transmission optical rotary encoder, it is formed to be a disk shape using a transparent resin material. Further, as described later, it is also possible to apply the code plate to a reflection encoder or a linear encoder.
In each pattern structure portion 20, a flat planar portion FL 21 and a non-planar portion DT 22 in which irregularities are formed on the surface thereof to have a non-planar shape are formed so as to have a rectangular shape having a longitudinal direction in the radial direction, respectively. Since the optical rotary encoder of the present embodiment is a transmission type, and in the planar portion 21 which has a flat surface, the code plate 10 is formed of a transparent material so that the light flux for detection is transmitted. On the other hand, in the non-planar portion 22 in which irregularities are formed on the surface to have a non-planar shape, the light flux for detection is totally reflected substantially when the light flux is irradiated at a predetermined angle.
The non-planar portion DT 22 is formed in an elongated rectangular shape so as to protrude from the planar portion FL 21 which is a flat plate surface of substantially planar. Further, the planar portion 21 is continuous with the part other than the pattern structure 20. In this sense, the side in the radial direction has a boundary which is in contact with the non-planar portion 22, the side in the circumferential direction does not have a clear boundary, and it may not have a rectangle shape. However, simply observing the pattern structure portion 20 which is ring-shaped, since the inner circle which is ring-shaped and the outer circle which is ring-shaped form substantially parallel two sides, it may be possible to say that it is a rectangle shape.
However, it is not necessary that both the planar portion FL 21 and the non-planar portion DT 22 have rectangular shapes, but it may be sufficient to have a condition in which they alternately across the region through which the light flux for detection is irradiated.
Further, in this embodiment, the non-planar portion 22 is protruding from the planar portion 21, and the bottom of the valley which is the concave portion is positioned at the same height as the planar portion 21. However, conversely, it is possible to form so that the non-planar portion 22 is disposed lower than the planar portion 21 so that the top portion is positioned at the height of the planar portion 21. Thus, any modification is possible in consideration of the condition of the injection molding process.
It is clear that the two concentric ring-shaped pattern structures 20 have different circumferential lengths to each other basically. However, in the multiple ring-shaped pattern structures 20 formed concentrically, it is formed so as to match the width and the spacing of the planar portion 21 and the non-planar portion 22 roughly between them, as a result, the pattern structure portion 20 of the inner circle has different numbers of the planar portion 21 and the non-planar portion 22 from those of the pattern structure portion 20 of the outer circle. Accordingly, the formation positions (angular position) of the planar portion 21 and the non-planar portion 22 are different between the inner circle and the outer circle, however, as described later, in the present invention, it is possible to easily change the formation positions of the non-planar portion 22 in the inner circle and the outer circle.
When it is set to match the width and the spacing of the planar portion 21 and the non-planar portion 22 roughly in the inner circle and the outer circle, it is possible to use the common electrical circuit, etc. which include the light-emitting element for detection and the sensor for receiving the light flux. When it is needed to form the planar portion 21 and the non-planar portion 22 in the inner circle at the same angular position as that in the outer circle, the widths and the spaces of the planar portion 21 and the non-planar portion 22 in the inner circle differ from those in the outer circle.
Further, in the present invention, the pattern structure portions 20 are formed in a ring shape at a plurality of the positions concentrically, however, it is not necessarily to be a plurality, but it may be a single. Further, it is not limited to be two, but it may be three or more.
In practice, the light flux for detection is irradiated at a predetermined position, and when the code plate 10 is rotated about the axis, the planar portion 21 and the non-planar portion 22 which are disposed in a ring shape enter the light flux path and go out from the light flux path alternately. In this sense, it can be said that the light flux for detection is not moved, but the light flux is scanned on the planar portion 21 and the non-planar portion 22, relatively.
In
As shown in the section view of
Each V-shaped structure 22a has a width of the non-planar portion 22 in the parallel direction and a width LD in the radial direction R. Further, the projected length of the slopes SL1 and SL2 for the surface plane of the code plate 10 are WF1 and WF2, respectively, the projected length of the top portion CN is WC. The top portion CN have a predetermined length due to a dullness caused by the molten resin because the molten resin is impenetrable to narrow gap of the mold. It is unavoidable in the resin molded component, however, it is possible to reduce the degree of dullness with the molding method of the code plate 10. For example, if it is cut in each code plate individually, it is possible to make the projected length WC of the top portion CN to below 2.0 μm. On the other hand, it consumes a relatively long time to form it, and it is difficult to form a mirror surface on the slope for the total reflection. Further, according to the imprinting method, the accuracy of the molded product for the mold may be improved, and it is possible to form a projected length WC of the top portion CN of below 2.0 μm similarly to the individual cutting method, however, it takes a relatively long time to form the one code plate. On the other hand, in terms of cost performance, the general injection molding has an advantage as the forming method for this kind of the code plate, however, the projected length WC of the top portion CN may be long compared to those by the two molding methods described above.
On the other hand, it is required that the non-planar portion 22 has a predetermined reflectance to use it as a product. There is almost no transmitting light at the slopes SL1 and SL2 because of the total reflection, however, it is not possible to achieve the total reflection at the top portion CN, and a part of the light flux may transmit. Therefore, it becomes a factor to reduce the reflectance in the non-planar portion 22.
Theoretically, in the two planar slopes SL1 and SL2 which form the V-shaped structure and the top portion CN, it is possible to calculate the degradation of the reflectance in accordance with the projected areas for the surface plane of each code plate 10. More specifically, since the light is totally reflected by the projected areas of the slopes SL1 and SL2 and is transmitted by the projected area of the top portion CN, it is possible to calculate the degradation of the reflectance by the ratio of the projected areas. Hereinafter, this degradation is represented by degradation rate DR. In order to use the device as a product, it is desired that the deterioration rate DR is equal to or less than 9%.
Now, it is defined that the lengths occupied by the slopes SL1 and SL2 for the surface of the code plate 10 are WF1 and WF2, respectively, and the length occupied by the top portion CN is WC. Since the width of the non-planer portion 22 is constant, the ratio of the projected areas of the slopes SL1 and SL2 and the top portion CN is WF1:WF2:WC. Therefore, the degradation rate DR is expressed as
DR=WC/(WF1+WC+WF2)
Accordingly, when it is assumed the length WC occupied by the top portion CN is a fixed value, the lengths WF1 and WF2 occupied by the slopes SL1 and SL2 may be increased to reduce the degradation rate DR.
In the present embodiment, the diameter of the code plate 10 is approximately 32 mm, the lengths of the planar portion 21 and the non-planar portion 22 in the parallel direction that is the circumferential direction are 30 μm, respectively, and the length in the longitudinal direction that is the radial direction is 260 μm. Since they have the same length in the parallel direction and are disposed alternately, it may be referred to as pitch in the following description. In this embodiment, the width WT of the planar portion 21 is determined to match with the width WR of the non-planar portion 22, however, it is not necessary to match.
In the code plate of this optical encoder, one V-shaped structure 1 is formed in one non-reflection portion DTPR to perform a high-precision encoding. More specifically, the non-planar portion DTPR of elongated rectangular shape is one V-shaped structure 1 of elongated shape, and the direction in which the rectangular shape is extending matches with the direction in which the V-shaped structure 1 is extending. In this case, it is obvious that the width LDPR of the V-shaped structure matches the width of the non-planar portion DTPR. Alternatively, it is also possible to form multiple V-shaped structures while maintaining the extending direction of the V-shaped structure, however, if the multiple V-shaped structures are formed, the width LDPR of the V-shaped structure becomes small compared to the width of the non-planar portion DTPR.
Now, as shown in
DRPR=WCPR/(WF1PR+WCPR+WF2PR).
When the code plate is formed by the injection molding method, the width of the non-planar portion is 30.0 μm, the length of the width LDPR of the V-shaped structure 1 is 30.0 μm, and the length of the top portion CNPR for the surface of the code plate is equal to or more than 2.83 μm. Accordingly, the degradation rate DRPR is expressed as
In other words, the degradation rate DRPR is equal to or more than 9.43%, and further improvement cannot be expected. Because, as far as the direction in which the V-shaped structure 1 is extending is consistent with the extending direction of the non-planar portion DTPR, it is not possible to make the width LDPR of the V-shaped structure larger than the width LDPR of the non-planar portion DTPR.
On the other hand, in the present invention, since the multiple V-shaped structures 22a are arranged in the direction in which the non-planar portion 22 is extending, the width LD of the V-shaped structure 22a is not limited by the width of the non-planar portion 22 in the parallel direction. As an example, when the width LD is 60 μm and the length WC of the top portion for the surface of the code plate is 2.83 μm, the degradation rate DR is expressed as
That is, the degradation rate DR is 4.72%, thus, it is found that the degradation rate can be improved greatly compared to that in the conventional device.
If it is desired that the degradation rate DR is set to 9%, the width LD of the V-shaped structure 22a may be determined to 31.4 μm. Even in the improvement upto 9%, there is a large difference in the yield depending on the required accuracy of the transmittance for the product. Further, from the sense of improvement of the performance, of course, it is also possible to set the width LD of the V-shaped structure 22a to equal to or more than 40.4 μm so that the degradation rate becomes equal to or lower than 7%.
Thus, it became possible to improve the deterioration rate DR compared to the conventional device by setting the width LD of each V-shaped structure 22a larger than the width of the non-planar portion 22 in the parallel direction.
In this embodiment, since a V-shaped structure 22a which becomes a mountain-shaped structure is adopted to form multiple convex or concave structures, as shown in
Next,
In this embodiment, the direction in which multiple V-shaped structures 22a are arranged is substantially perpendicular to the parallel direction. In other words, the direction in which the V-shaped structure 22a are arranged is orthogonal to the direction in which the top portion CN is extending. Now, it is called inclination of the V-shaped structure 22a, and it is 90° when it is orthogonal.
In the devices shown in
In the embodiment described above, the present invention is applied to the code plate of the transmission optical rotary encoder. More specifically, the pattern structure portion 20 in which the planar portion 21 and the non-planar portion 22 are formed alternately is formed in a ring shape, further, in the present embodiment, the pattern structure portion 20 is formed in a ring shape at multiple positions concentrically.
However, the present invention is applicable similarly in the code plate 30 of the linear encoder shown in
In the embodiment described above, the transmission optical rotary encoder is described, however, it is also true in the reflective optical encoder similarly. In the reflective optical encoder, the reflective material is coated on the surface of the code plate so that the light is totally reflected in the planar portion to a predetermined direction in which the light receiving elements are provided to receive the light. In this case, the light receiving element detects the bright section. By contrast, in the non-planar portion, the light is totally reflected in a direction in which the light receiving elements are not provided so that the light receiving element can detect the dark section.
However, some of the reflected light may be received by the light receiving element because of the dullness formed at the top portion in the non-planar portion. Further, in this case, the top portion formed by the injection molding may not be a size less than around a predetermined value, as a result, there is some limitation in the degradation rate of the non-reflectance in the region in which it must be non-reflective due to the limitation of the width of the V-shaped structure.
However, by applying the present invention, the width of the V-shaped structure is not limited by the width of the non-planar portion in the arrangement direction thereof so that it is possible to achieve further reduction of the degradation rate of the non-reflectance.
Further, the V-shaped structure is employed for the convex or concave structure, however, as far as it is possible to eliminate the deterioration of the permeability and reflectivity caused by the dullness at the top portion, it is not limited to the V-shaped structure, but a concave or convex structure of other shape can be applied. Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.
Note that, this invention is not limited to the above-mentioned embodiments. Although it is to those skilled in the art, the following are disclosed as the one embodiment of this invention.
While the invention has been particularly shown and described with respect to preferred embodiments thereof, it should be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the sprit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-108899 | May 2013 | JP | national |
