JP2012237616A - Optical encoder and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical encoder capable of maintaining a stable detection accuracy even at a high temperature of around 100 to 130°C and under environment in which possibility of touching also steam, cutting oil, and the like, and to secure a sufficient service life of a mold for a code plate and high reliability of an obtained molding (the code plate) in a method for manufacturing the code plate used for the optical encoder.SOLUTION: An optical encoder comprises a light projection part, a light-receiving part, and a code plate made of a resin material, and the code plate has a code pattern including a V-shaped groove or a V-shaped protrusion. The resin material has a refraction index, with respect to light of a wavelength used for detection at 130°C, equal to or more than 1.6, and a glass dislocation point equal to or less than 190°C.

Description

  The present invention relates to an optical encoder and a manufacturing method thereof. More specifically, the present invention relates to an optical encoder using a code plate made of a resin material regardless of a rotating shaft or a linear scale, and a manufacturing method thereof.

  Conventionally, as a code plate of an optical encoder having such a structure, a resin code including a flat portion that transmits light supplied from a light source as it is and a V-shaped protrusion or V-shaped groove that does not transmit light supplied from the light source. The board is known. In the resin code plate having V-shaped protrusions or V-shaped grooves, when the V-shaped inclination angle becomes equal to or larger than the critical angle, total reflection of light supplied from the light source occurs. In the optical encoder, for example, in the case of a method of detecting the transmitted light of the code plate, the flat portion of the code plate is detected as a bright portion and the V-shaped portion (V-shaped projection portion or V-shaped groove portion) is detected as a dark portion. On the other hand, in the case of the method of detecting reflected light, the flat part is detected as a dark part and the V-shaped part is detected as a bright part. As a material for the resin code plate, transparent resins such as polymethyl methacrylate (PMMA) and polycarbonate (PC) are generally used.

  However, a general application target of the optical encoder having such a configuration is an industrial motor. Around the rotating shaft of industrial motors, the temperature tends to be high, and there is a risk of contact with steam, cutting oil, and the like. Therefore, the resin material used for the cord plate is required to have high heat resistance and oil resistance.

  In addition, in a high-precision encoder, the width and height of the V-shaped portion become as fine as several μm to several tens of μm, and thus it is difficult to completely transfer the V-shaped tip shape by molding. The tip of is rounded. In the rounded portion, the angle of the wall surface with respect to the incident light is reduced, and when the angle is below the critical angle, leaked light that is transmitted without being reflected is generated. This leaked light becomes a cause of a decrease in the detection accuracy of the encoder. Since the refractive index of a resin generally decreases at a high temperature, the critical angle decreases and the leakage light tends to increase under a high temperature environment. For this reason, in the polycarbonate generally used conventionally, the encoder used for industrial uses, such as FA apparatus, had the situation where it was difficult to maintain detection accuracy in a high temperature environment exceeding 100 ° C. In industrial applications, high temperature steam, cutting oil, etc. may be touched. For this reason, it is necessary to perform coating on the cord plate using the polycarbonate resin, which causes an increase in cost.

  Patent Document 1 (Japanese Patent Laid-Open No. 2004-325231) uses polyetherimide, polyethersulfone, and polyphenylsulfone, which have high heat resistance and oil resistance, as a material for the cord plate as a countermeasure against such problems. It has been proposed to do.

JP 2004-325231 A

  The polyetherimide, polyethersulfone, and polyphenylsulfone described in Patent Document 1 have glass transition points (Tg) of 217, 225, and 220 ° C., respectively, and are the highest among thermoplastic resins. Low fluidity makes it difficult to fill (transfer) a resin into a fine code pattern such as a V-shaped projection. For this reason, it was necessary to raise the melt resin temperature to 400 ° C. or higher and to raise the mold temperature to a very high temperature of 210 ° C. or higher near Tg to improve the transferability of the material.

  In this case, when the mold temperature and the temperature of the resin material become high, the steel material of nickel or nickel phosphorus generally used for the optical component molding die is exposed to a high temperature for a long time. At that time, crystallization of the steel material (crystallization temperature of nickel phosphorus of 300 to 370 ° C.) proceeds, and the hardness of the steel material becomes high and brittle. As a result, peeling of the steel material is likely to occur every time molding is repeated, and the life of the mold is shortened. Further, it becomes difficult to obtain a molded product having a code pattern as designed, and the reliability of the molded product is lowered. For this reason, the method described in Patent Document 1 has a problem that it is not suitable for mass production.

  The present invention has been made to solve the above-described problems, and is stable even in an environment where there is a possibility of contact with steam, cutting oil, etc. at a high temperature of about 100 ° C. to 130 ° C. An optical encoder capable of maintaining detection accuracy is provided, and in the production of a code plate used for the optical encoder, a sufficient life of a code plate mold and a high molding product (code plate) are obtained. The purpose is to ensure reliability.

The present invention is an optical encoder including a light projecting unit, a light receiving unit, and a code plate made of a resin material,
The code plate has a code pattern including a V-shaped groove or a V-shaped projection,
The resin material is an optical encoder characterized in that a refractive index with respect to light having a wavelength used for detection at 130 ° C. is 1.6 or more and a glass transition point is 190 ° C. or less.

  The glass transition point of the resin material is preferably 140 ° C. or higher. The resin material preferably contains at least one selected from the group consisting of fluorene-based polyester, polysulfone, and transparent polyamide.

The light having a wavelength used for the detection is preferably infrared light.
A method for manufacturing an optical encoder including a light projecting unit, a light receiving unit, and a code plate made of a resin material,
The code plate has a code pattern including a V-shaped groove or a V-shaped projection,
The resin material has a refractive index with respect to light having a wavelength used for detection at 130 ° C. of 1.6 or more, and a glass transition point of 190 ° C. or less.
The present invention also relates to a method for manufacturing an optical encoder, comprising the step of forming the code plate having the code pattern by molding the resin material at a temperature of 360 ° C. or less.

  In the present invention, by using a resin material for the code plate that can maintain a refractive index of 1.6 or higher even in a 130 ° C. environment, the amount of leakage light in a high temperature environment can be suppressed and stable detection accuracy can be maintained. An optical encoder is provided. In addition, since it can be molded at a resin temperature of 360 ° C. or lower, the deterioration of the mold material (nickel, nickel phosphorus, etc.) (embrittlement due to crystallization) is suppressed, and a sufficient life of the code plate mold The life of the mold can be ensured, and high reliability of the obtained molded product (code plate) can be ensured.

  Further, when a resin material having a glass transition point of 140 ° C. or higher and excellent chemical resistance is used, an optical encoder code plate having excellent durability can be obtained without coating. Such a cord plate does not discolor or deform even when it comes into contact with steam or cutting oil.

It is a figure showing the relationship between the resin temperature at the time of shaping | molding of a code | cord | chord board, metal mold | die temperature, and the metal mold | die surface X-diffraction profile after shaping | molding. 1 is a schematic diagram illustrating an optical encoder according to a first embodiment. FIG. 3 is an enlarged view of a code pattern portion of the optical encoder according to the first embodiment. 6 is a schematic diagram illustrating an optical encoder according to Embodiment 3. FIG. FIG. 10 is a schematic diagram illustrating an optical encoder according to a fourth embodiment. It is a figure which shows the relationship between each resin material, a glass transition temperature, and a refractive index.

  FIG. 1 is a diagram showing a relationship between a resin temperature and a mold temperature at the time of molding a code plate and a mold surface X-resolved diffraction profile after molding. When a cord disk is molded using polyetherimide based on Patent Document 1, the presence of a crystallized product is confirmed on the mold surface after molding, and the mold V protrusion is damaged. On the other hand, no crystallized material is detected on the mold surface after molding using the resin according to the present invention, and no damage occurs. As shown in FIG. 1, it can be seen that when the resin temperature at the time of molding the code plate exceeds 360 ° C., the mold life sharply decreases. The present invention has been devised based on such new findings obtained by the present inventors. That is, by molding the resin material at a temperature of 360 ° C. or less to produce a code plate having a code pattern, it is possible to sufficiently maintain the mold life.

  In the present invention, even when molded at a temperature of 360 ° C. or less, a glass transition point is a resin material that has sufficient fluidity and can be filled (transferred) into a fine code pattern such as a V-shaped protrusion. A resin material having a temperature of 190 ° C. or lower is used. Moreover, in order to obtain the code | cord plate which can maintain high heat resistance also in a use environment, it is preferable to use the resin material whose glass transition point is 140 degreeC or more.

  In addition, since the resin material used in the present invention has a refractive index of 1.6 or more with respect to light having a wavelength used for detection at 130 ° C., the amount of leakage light in a high temperature environment is suppressed and stable detection accuracy is maintained. An optical encoder is provided.

(Embodiment 1)
FIG. 2 is a schematic diagram showing the optical encoder of the present embodiment. This encoder is a rotary encoder, and is used for a sensor for converting a mechanical displacement amount of rotation into an electric signal and processing the signal to detect a position / speed. As shown in FIG. 2, a code disk 1 that is a code plate of the present embodiment has a code pattern 2 on one side. A light receiving unit 4 is installed on the code pattern 2 side of the code disk 1, and a lens unit 5 and a light projecting unit 6 are installed on the opposite side of the light receiving unit 4.

  FIG. 3 is an enlarged view of the code pattern 2. The code pattern 2 has a V-shaped projection 3. The inclination angle (α shown in FIG. 3) of the V-shaped projection 3 is set to a value larger than the critical angle θ = sin−1 (1 / n) determined by the refractive index n of the material. The code pattern 2 is concentrically divided into several types of pattern areas, and a V-shaped protrusion width and a pitch distance are set for each pattern area. In a high-precision optical encoder used for industrial use, the V-shaped protrusion width is often set to 50 μm or less. The code disk 1 is attached to a rotating shaft 7 such as a motor, and rotates in synchronization with the rotation of the rotating shaft 7.

  A light emitting device such as an LED is used for the light projecting unit 4. For example, infrared light 8 having a wavelength of 800 nm to 1000 nm is emitted from the light projecting unit 4. The emitted infrared light is collimated by the lens unit 5 and enters the code disk 1. When the infrared light 8 is incident on the flat portion of the code pattern 2, it passes through the code disk 1 and reaches the light receiving portion 4. When the infrared light 8 is incident on the V-shaped protrusion 3 of the code pattern 2, total reflection occurs and the light is shielded. Thus, a transmission / light-shielding pattern is formed as the code disk 1 rotates. When the width or pitch of the V-shaped projection 3 is changed, the amount of infrared light 8 reaching the light receiving unit 4 becomes a sine wave, which is converted into an electric signal by the light receiving unit 4 and the rotational position of the code disk 1 is detected. .

  The code plate is formed by pouring molten resin into a mold by injection molding. Although it is desirable that the inclination angle of the V-shaped protrusion 3 is ideally uniform, in reality, the resin is not completely filled up to the tip of the protrusion, and the tip is rounded. In the rounded shape portion, the tilt angle decreases, and light leaks when the angle is less than the critical angle. When the amount of leakage light changes, the offset amount (DC) with respect to the sine wave (AC) component of the electrical signal fluctuates, so that the detection characteristics such as position and speed are deteriorated. The resin material has a characteristic that the refractive index decreases when the temperature rises, and the amount of leakage light increases when the temperature of the use environment rises. For this reason, the encoder characteristics may deteriorate at high temperatures.

  When the cord disk 1 is molded using polycarbonate as in the prior art, the temperature of the resin filled in the mold is set to 290 ° C to 310 ° C, and the temperature of the mold is set to 135 ° C to 145 ° C. The In the cord disk 1 made of polycarbonate, when the inclination angle of the V-shaped projection 3 is set between 40 ° and 45 °, the ratio of the amplitude of the AC component to the DC component of the optical signal (AC / DC ratio) is , About 58-59% at room temperature. In order to maintain the position detection accuracy of the optical encoder, the AC / DC ratio is desirably 58% or more.

  However, the refractive index of polycarbonate for infrared light is about 1.57 at room temperature, but drops to about 1.56 at a temperature of 130 ° C. For this reason, when the temperature of the use environment is 130 ° C., the amount of leakage light due to a decrease in the refractive index of the resin increases the AC / DC ratio to less than 58%, which may deteriorate the detection accuracy. Further, since polycarbonate changes color and deforms when it is exposed to high-temperature steam and cutting oil, it is necessary to coat the cord disk 1 with a transparent coating material by vapor deposition or the like.

  On the other hand, as described in Patent Document 1, when the cord disk 1 is molded using polyetherimide, the molding temperature is such that the resin temperature is 400 ° C. or higher and the mold temperature is 210 ° C. or higher. Must be set to For this reason, crystallization of the mold material progresses while molding is continued, and the hardness becomes high and becomes brittle. Further, peeling of the steel material is likely to occur each time the molding is repeated, so that it is difficult to obtain a molded product (code plate) in which a designed code pattern is formed, and the life of the mold is shortened. It was.

  On the other hand, in the present invention, as the material of the code plate, the refractive index for light having a wavelength used for detection at 130 ° C. (such as infrared light) is 1.6 or more, and the glass transition point is 190 ° C. or less. A resin material is used. As for this resin material, it is more preferable that a glass transition point is 140 degreeC or more. Examples of such a resin material include fluorene polyester, polysulfone, and transparent polyamide (see FIG. 6). Examples of the fluorene-based polyester include OKP4 and OKP4HT manufactured by Osaka Gas Chemical. Examples of the polysulfone include P-3700HC manufactured by Solvay Advanced Polymers. Examples of the transparent polyamide include FE5577 manufactured by Ms. Chemie Japan.

  For example, when the cord disk 1 is molded using fluorene polyester, the temperature of the resin filled in the mold is set to 270 ° C. to 300 ° C., and the temperature of the mold is set to 130 ° C. to 140 ° C. . The refractive index of fluorene-based polyester resin with respect to infrared light is about 1.62 at room temperature and about 1.61 at 130 ° C. For this reason, the AC / DC ratio at room temperature is 60% or more, and it can be maintained at 58% or more even at a temperature of 130 ° C. Further, since the fluorene-based polyester does not discolor or deform even when it is exposed to high-temperature steam or cutting oil, it is not necessary to coat the cord plate. Furthermore, since the molding temperature is relatively low, which is close to the molding temperature of polycarbonate, there is no reduction in mold life.

  As described above, according to Embodiment 1 of the present invention, it is possible to maintain a stable detection accuracy even in a high temperature environment, and it is possible to obtain an optical encoder having excellent durability even without a coating. Moreover, the lifetime of a metal mold | die can be maintained and a molded article (code board) with high shaping | molding reliability can be obtained.

(Embodiment 2)
In the present embodiment, polysulfone or transparent polyamide is used as the resin material constituting the cord disk 1. Other aspects are the same as in the first embodiment. However, when polysulfone is used, the temperature of the resin filled in the mold is set to 340 ° C. to 360 ° C., and the temperature of the mold is set to 166 ° C. to 171 ° C. Moreover, when using transparent polyamide, the temperature of the resin with which a metal mold | die is filled is set to 290 degreeC-310 degreeC, and the temperature of a metal mold | die is set to 155 degreeC-170 degreeC. In the present embodiment, an optical encoder having the same characteristics as in the first embodiment is obtained.

(Embodiment 3)
In the present embodiment, the present invention is used for an optical encoder that detects the reflected light of a code disk. Other aspects are the same as in the first embodiment.

  FIG. 4 is a schematic diagram showing the optical encoder of the present embodiment. The light receiving unit 4 and the light projecting unit 6 are installed on the same side (code pattern 2 side) with respect to the code disc 1, and the light receiving unit 4 detects the infrared light 8 reflected by the code disc 1. Function as an encoder. The resin material constituting the cord disk 1 and the method for forming the cord disk 1 are the same as those in the first and second embodiments. In the present embodiment, an optical encoder having the same characteristics as in the first embodiment is obtained.

(Embodiment 4)
The optical encoder of the present embodiment is a linear encoder and is used for a sensor or the like that detects a linear mechanical displacement amount. That is, a linear code plate is used instead of the code disc 1 in the above embodiment.

  FIG. 5 shows a schematic diagram of the optical encoder of the present embodiment. As shown in FIG. 5, the linear code plate 9 has a code pattern 2 on one side thereof. The light receiving unit 4 is installed on the code pattern 2 side of the linear code plate 9, and the light projecting unit 6 and the lens unit 5 are installed on the opposite side of the light receiving unit 4. The optical signal output method is the same as that of the optical encoder described in the first embodiment. A transmission / shading pattern is formed as the linear code plate 9 moves horizontally, and the position of the linear code plate 9 is detected. . The resin material constituting the linear code plate 9 and the method for forming the linear code plate 9 are the same as those in the first embodiment. In the present embodiment, an optical encoder having the same characteristics as in the first embodiment is obtained.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 code disk, 2 code pattern, 3 V-shaped protrusion, 4 light receiving part, 5 lens part, 6 light projecting part, 7 rotation axis, 8 infrared light, 9 linear code board.

Claims (5)

An optical encoder including a light projecting unit, a light receiving unit, and a code plate made of a resin material,
The code plate has a code pattern including a V-shaped groove or a V-shaped projection,
The optical encoder is characterized in that the resin material has a refractive index of 1.6 or more for light having a wavelength used for detection at 130 ° C, and a glass transition point of 190 ° C or less.   The optical encoder according to claim 1, wherein the glass transition point of the resin material is 140 ° C. or higher.   The optical encoder according to claim 1, wherein the resin material includes at least one selected from the group consisting of fluorene-based polyester, polysulfone, and transparent polyamide.   The optical encoder according to claim 1, wherein the light having a wavelength used for the detection is infrared light. A method for manufacturing an optical encoder including a light projecting unit, a light receiving unit, and a code plate made of a resin material,
The code plate has a code pattern including a V-shaped groove or a V-shaped projection,
The resin material has a refractive index with respect to light having a wavelength used for detection at 130 ° C. of 1.6 or more, and a glass transition point of 190 ° C. or less.
A method for manufacturing an optical encoder, comprising a step of forming the code plate having the code pattern by molding the resin material at a temperature of 360 ° C. or less.

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