JP2004198179A - Optical encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical encoder which reduces a detection error by reducing attachment of water to its optical components. <P>SOLUTION: A substance having water-repellence or hydrophilic function is caused to attach to slits in the optical encoder. It is desirable that PTFE should be used as a substance having the water-repellence function. It does not matter if either cadmium-tellurium or molybdenum sulfide is used as a substance having the hydrophilic function. It does not matter if any one of titanium oxide, tin oxide, zinc oxide, tungsten oxide, and cadmium-cerium is used, as a substance having photocatalytic function, and if a light emitting element 3 whose emitting light wavelength is in the blue region, or shorter than those. It does not matter if the optical encoder is housed in a housing case, and the housing case is charged with an adsorbent 7. A reading error can be diminished since the optical system is not clouded up with water droplets, even if the optical encoder is in a moisture condensing environment. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical encoder used for displacement measurement and angle measurement.
[0002]
[Prior art]
The optical encoder is basically a first main scale having an optical slit of a predetermined pitch, an index scale disposed opposite to the first main scale and having a second optical slit, and a light emitting element for irradiating the main scale with light. And a light receiving element that transmits or reflects through the optical slit of the main scale and receives light transmitted through the optical slit of the index scale.
This type of optical encoder is susceptible to detection errors due to elements that disturb the optical system from the outside, such as dust. Often, only the part is housed in a storage case, so that it is used in a so-called closed state (for example, see Patent Document 1).
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-9762 (Page 1-2, FIG. 1)
[0004]
[Problems to be solved by the invention]
By the way, the above-mentioned optical encoder has a problem that dew condensation easily occurs due to hermeticity, and when moisture adheres to the optical component, a detection error occurs due to clouding of the optical component.
Therefore, the present invention has been made in view of such a problem, and an object of the present invention is to provide an optical encoder in which adhesion of moisture to an optical component is reduced and a detection error is reduced.
[0005]
[Means for Solving the Problems]
To solve the above problems, the present invention is configured as follows.
(1) An optical encoder including a light-emitting element, a light-receiving element, a first slit having a predetermined pitch, and a second slit disposed to face the slit with a predetermined gap movable relative to the slit. A substance having a water repellent or hydrophilic function is attached to the slit.
(2) The substance having the water repellent function is PTFE.
(3) The substance having a hydrophilic function has a photocatalytic function.
(4) The substance having a photocatalytic function is cadmium-tellurium or molybdenum sulfide.
(5) The substance having a photocatalytic function is any one of titanium oxide, tin oxide, zinc oxide, tungsten oxide, and cadmium-cerium.
(6) The emission wavelength range of the light-emitting element according to (5) is blue or a wavelength shorter than that.
(7) The optical encoder described above is housed in a storage case, and an adsorbent is sealed in the storage case.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a sectional view showing the internal structure of the optical encoder of the present invention. In the figure, 1 is a main slit, 2 is an index slit, 3 is a light emitting element, 4 is a light receiving element, 5 is a rotating shaft, 6 is a storage case, and 7 is an adsorbent.
The main slit 1 is attached to the end of the rotating shaft 5 inside the storage case 6. Through this main slit 1, a light emitting element 3 is arranged on one side, and an index slit 2 and a light receiving element 4 are arranged on the other side. FIG. 2 is a diagram showing the operation of the optical encoder. The main slit 1 rotates together with the rotation shaft 5, and the fixed index slit 2 is engraved with light and dark stripes at the same pitch as the main slit 1. Therefore, when the light transmitting portions of the main slit 1 and the index slit 2 overlap with the straight line from the light receiving element 4 to the light emitting element 3 due to the rotation of the rotation shaft 5, the amount of received light becomes maximum and the light of the main slit 1 is When the portion that does not transmit is on the straight line, the amount of received light is minimized. The signal of the amount of received light is processed by a processing circuit (not shown) to obtain information on the angle of the rotation axis. Here, the surfaces of the optical system of the main slit 1, the index slit 2, and the light receiving element 4 were coated with PTFE. As a result, even when dew condensation occurs inside the storage case 6, the conventional reading error rate is reduced to 50% or less.
By applying the adsorbent 7 inside the storage case 6, the conventional reading error rate was further reduced to 50% or less even when the inside of the storage case 6 was dewed.
[0007]
(Second embodiment)
The configuration of the second embodiment is the same as that of the first embodiment, but the surfaces of the optical system of the main slit 1, the index slit 2, and the light receiving element 4 are coated with molybdenum disulfide. As a result, even when dew condensation occurs inside the storage case 7, the conventional reading error rate becomes 30% or less. When a film forming technique such as a vapor deposition method, a sputtering method or a plating method is used when coating molybdenum disulfide, the reading error rate is further reduced by half.
By applying the adsorbent 7 inside the storage case 6, the conventional reading error rate was further reduced to 50% or less even when the inside of the storage case 6 was dewed. When the adsorbent 7 is applied, the effect is further improved by applying molybdenum disulfide to a portion of the light-emitting element irradiated with the light source, such as the inner surface of the storage case.
In this embodiment, the surface of the optical system of the main slit 1, the index slit 2 and the light receiving element 4 is coated with molybdenum disulfide. Also obtained similar results.
[0008]
(Third embodiment)
The configuration of the third embodiment is the same as that of the first embodiment except that the surfaces of the main slit 1, the index slit 2 and the optical system of the light receiving element 4 are coated with titanium dioxide. The light emitting element and the light receiving element used were those in the blue wavelength range. As a result, even when dew condensation occurs inside the storage case 6, the conventional reading error rate becomes 30% or less. When a film forming technique such as a vapor deposition method, a sputtering method or a plating method is used when coating titanium dioxide, the reading error rate is further reduced by half. By applying the adsorbent 7 inside the storage case, the conventional reading error rate was further reduced to 50% or less even when the inside of the storage case 6 was dewed. When the adsorbent 7 is applied, the effect is further improved by applying titanium dioxide to a portion of the light emitting element irradiated with the light source, such as the inner surface of the storage case.
In this embodiment, the surface of the optical system of the main slit 1, the index slit 2, and the light receiving element 4 is coated with titanium dioxide. However, the same applies when tin dioxide, zinc oxide, or oxide is coated instead of titanium dioxide. Is obtained.
This embodiment also has an effect of improving the detection angle resolution as compared with the conventional example and the first and second embodiments.
[0009]
Although the above embodiments have been described with reference to a rotary optical encoder as an example, a so-called linear type which detects displacement based on the same principle can be applied. Also, the case where the optical encoder is stored in the storage case has been described. However, the invention is not limited to the case where only the optical encoder portion is stored in the storage case. It is also effective for what you are taking.
[0010]
【The invention's effect】
As described above, according to the optical encoder of the present invention, since a substance having water repellency or hydrophilicity is applied to the optical system, even in an environment where the optical encoder is condensed, the optical system can reduce the reading error without fogging with water droplets. Can be eliminated. Further, when an adsorbent is used inside the storage case, the humidity inside the storage case can be kept low. This effect is particularly remarkable when using titanium dioxide, tin dioxide, zinc oxide or tungsten oxide having a photocatalytic function. Further, when the substance having the photocatalytic function is used, the organic gas generated from the constituent parts is also decomposed, and there is an effect that the life of the optical encoder can be extended. In addition, when a substance having a photocatalytic function is applied to a portion where the light emitting element is irradiated inside the storage case, the effect of maintaining low humidity or the effect of reducing organic gas becomes more remarkable.
[Brief description of the drawings]
FIG. 1 is a side sectional view of an optical encoder showing an embodiment of the present invention. FIG. 2 is a perspective view showing the configuration of an optical encoder.
DESCRIPTION OF SYMBOLS 1 Main slit 2 Index slit 3 Light emitting element 4 Light receiving element 5 Rotating shaft 6 Storage case 7 Adsorbent

Claims (7)

A light-emitting element, a light-receiving element, a first slit having a predetermined pitch, and an optical encoder including a second slit arranged to face the slit with a predetermined gap movable relative to the slit;
An optical encoder, wherein a substance having a water-repellent or hydrophilic function is attached to the slit. The optical encoder according to claim 1, wherein the substance having the water repellent function is PTFE. The optical encoder according to claim 1, wherein the substance having a hydrophilic function has a photocatalytic function. The optical encoder according to claim 3, wherein the substance having a photocatalytic function is cadmium-tellurium or molybdenum sulfide. The optical encoder according to claim 3, wherein the substance having a photocatalytic function is any one of titanium oxide, tin oxide, zinc oxide, tungsten oxide, and cadmium-cerium. The optical encoder according to claim 3, wherein a light emission wavelength range of the light emitting element is blue or shorter in wavelength. The optical encoder according to claim 1, wherein the optical encoder is housed in a storage case, and an adsorbent is sealed in the storage case.

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