JP2018031834A - Optical lens for encoders - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical lens that allows an encoder to be easily reduced in size.SOLUTION: An optical lens is composed of an SnO-POglass with a refractive index of 1.65 or more, has a height of 5 mm or less, and contains, as its composition, SnO of 33.5-90 mol%, PO+SiO2+BOof 0.1-66.5 mol%, with a glass transition point of 200°C or more, a thermal expansion coefficient at 30-200°C of 200×10/°C or less, a Young's modulus of 60 GPa or less, and a photoelastic constant of 2×10-12/Pa or less.SELECTED DRAWING: None

Description

  The present invention relates to an optical lens for an encoder.

  With the recent development of robot engineering, it is important to strictly control the driving of joints (axes) in medical and industrial robots. For the axis control, a magnetic or optical encoder is used. Since a robot or the like drives many axes, the encoder needs to be as small as possible. In an optical encoder, light from a light emitting diode is collimated by a lens, and the collimated light passes through a turntable and is received by a light receiver. As a lens for collimating light, use of a resin lens has been studied. (For example, see Patent Document 1)

JP 2008-003466 A

  However, since the resin lens has a low refractive index, there is a problem that it is difficult to miniaturize the encoder, and it is difficult to use it for an encoder used in a robot or the like.

  The present invention has been made in view of such a situation, and an object thereof is to provide an optical lens in which an encoder can be easily miniaturized.

  The optical lens for an encoder of the present invention is made of glass having a refractive index of 1.65 or more and has a height of 5 mm or less. By using a glass with a high refractive index as a lens used for the encoder, the focal length is shortened, so that the encoder can be easily downsized.

The optical lens for encoder of the present invention is preferably made of SnO—P ₂ O ₅ glass. SnO—P ₂ O ₅ glass is suitable as the optical lens of the present invention because it easily achieves a high refractive index.

The optical lens for an encoder of the present invention is composed of glass containing SnO 33.5 to 90% and P ₂ O ₅ + SiO ₂ + B ₂ O ₃ 0.1 to 66.5% in terms of a composition. preferable. Here, “P ₂ O ₅ + SiO ₂ + B ₂ O ₃ ” means the total content of P ₂ O ₅ , SiO ₂ and B ₂ O ₃ .

  The optical lens for encoder of the present invention is preferably made of glass having a glass transition point of 200 ° C. or higher. In this way, even at high temperatures, it is difficult to deform and the focal length is unlikely to change.

The optical lens for an encoder of the present invention is preferably made of glass having a thermal expansion coefficient of 200 × 10 ⁻⁷ / ° C. or less in the range of 30 to 200 ° C. In this way, it is difficult for the focal length to change due to deformation due to temperature changes.

  The optical lens for encoder of the present invention is preferably made of glass having a Young's modulus of 60 GPa or less.

The optical lens for an encoder of the present invention is preferably made of glass having a photoelastic constant of 2 × 10 ⁻¹² / Pa or less.

  In the optical lens for encoder of the present invention, it is preferable that an antireflection film is provided on the lens surface.

  According to the present invention, it is possible to provide an optical lens in which the encoder can be easily miniaturized.

It is a typical sectional view showing the basic structure of an encoder. It is typical sectional drawing which shows one Embodiment of the optical lens of this invention.

  First, the principle and structure of the encoder will be described with reference to FIG. The encoder is a sensor that outputs a mechanical position change and speed of a rotating mechanism such as a motor by an electric signal. Specifically, the diffused light emitted from the light emitting diode 1 is collimated by the optical lens 2. The collimated light transmitted through the lens 2 is transmitted or blocked by a turntable 5 having a light transmitting portion 5a and a light blocking portion 5b provided on the rotating shaft 4 of the rotating mechanism 3. The light transmitted through the light transmission part 5 a of the rotating disk 5 is detected by the light receiver 6. The light receiver 6 outputs an electrical signal corresponding to the amount of received light. With this electric signal, information on the mechanical position change and speed of the rotating mechanism 3 can be obtained.

  Next, the optical lens for encoder of the present invention will be described.

  The optical lens for encoder of the present invention is preferably made of glass having a refractive index (nd) of 1.65 or more and 1.75 or more, particularly 1.85 or more. If the refractive index is too low, the focal length becomes long, and it becomes difficult to miniaturize the encoder.

  FIG. 2 is a schematic cross-sectional view according to one embodiment of the optical lens of the present invention. The height H (maximum thickness) of the lens is 5 mm or less, preferably 4 mm or less, 3 mm or less, 2 mm or less, 1 mm or less, and particularly preferably 0.8 mm or less. If the lens height is too large, it will be difficult to miniaturize the encoder. The lens height H / lens width W is preferably 1 or less, 0.8 or less, and particularly preferably 0.6 or less. If the lens height H / lens width W is too large, it is difficult to reduce the size of the encoder. The lens shape is not particularly limited, but a plano-convex shape is preferable. The plano-convex shape makes it easier to collimate light.

  The optical lens for an encoder of the present invention is preferably made of glass having a glass transition point of 200 ° C. or higher, 220 ° C. or higher, particularly 240 ° C. or higher. If the glass transition point is too low, the glass transition point is likely to be deformed at a high temperature, and the focal length is likely to change. The upper limit is not particularly limited, but considering press formability, it is preferably 650 ° C. or lower, 600 ° C. or lower, particularly 500 ° C. or lower.

The optical lens for an encoder of the present invention is made of glass having a thermal expansion coefficient of 200 × 10 ⁻⁷ / ° C. or lower, 180 × 10 ⁻⁷ / ° C. or lower, particularly 160 × 10 ⁻⁷ / ° C. or lower in the range of 30 to 200 ° C. It is preferable to become. When the thermal expansion coefficient is too large, deformation due to temperature change becomes large, and the focal length changes easily.

  The optical lens for an encoder of the present invention is preferably made of glass having a Young's modulus of 60 GPa or less, 50 GPa or less, 45 GPa or less, particularly 40 GPa or less. If the Young's modulus is too large, it is difficult to release from the mold, and it is easy to crack during cooling.

The optical lens for encoder of the present invention has a photoelastic constant of 2 × 10 ⁻¹² / Pa or less, 1.5 × 10 ⁻¹² / Pa or less, 1.0 × 10 ⁻¹² / Pa or less, particularly 0.5 × 10. It is preferable to consist of glass of ^-12 / Pa or less. If the photoelastic constant is too large, focus deviation due to aberration tends to occur.

For the purpose of improving the light transmittance, an antireflection film may be provided on the lens surface of the encoder optical lens. As the antireflection film, an MgF ₂ film, a dielectric multilayer film, or the like can be used.

The glass is preferably SnO—P ₂ O ₅ glass. SnO—P ₂ O ₅ glass has optical properties of high refractive index and high dispersion.

The _SnO-P 2 _{O 5} based glass, in mol%, SnO _33.5-90%, those containing _{2 O 3 + SiO 2 0.1~66.5%} P 2 O 5 + B preferred. Below, the reason which specified content of each component as mentioned above is demonstrated. Unless otherwise specified, “%” means “mol%” in the following description of component contents.

  SnO is a component for achieving high refractive index and high dispersion optical characteristics and improving chemical durability. The SnO content is preferably 33.5 to 90%, 35 to 88%, 40 to 86%, 50 to 85%, particularly 57.5 to 83%. When the content of SnO is too small, it becomes difficult to achieve high refractive index characteristics, and the weather resistance and chemical durability tend to decrease. On the other hand, when there is too much content of SnO, there exists a tendency for devitrification resistance to fall.

P ₂ O ₅ , B ₂ O ₃ and SiO ₂ are components constituting the skeleton of the glass. Moreover, it is a component which raises the transmittance | permeability of glass, can suppress the transmittance | permeability fall near ultraviolet region, or can shift an absorption edge to the low wavelength side. In particular, in the case of a glass having a high refractive index, the effect of improving the transmittance due to these components is easily obtained. It also has the effect of suppressing devitrification. The total content of P ₂ O ₅ , B ₂ O ₃ and SiO ₂ is 0.1 to 66.5%, 10 to 60%, 15 to 57.5%, 20 to 55%, particularly 25 to 47 in total. % Is preferred. If the content of these components is too small, the above-described effects are hardly obtained. On the other hand, if the content is too large, the content of SnO ₂ becomes relatively small, and the refractive index tends to decrease.

_A preferable content of each component of the _{P 2 O 5, B 2 O} 3 and SiO ₂ are as follows.

The content of P ₂ O ₅ is preferably 0.1 to 66.5%, 1 to 60%, 3 to 57.5%, 4 to 55%, 5 to 50%, particularly preferably 10 to 47%. When the content of P ₂ O ₅ is too large, the refractive index tends to decrease. Further, weather resistance and chemical durability are likely to be lowered.

The content of B ₂ O ₃ is 0 to 66.5%, 0.1 to 66.5%, 1 to 60%, 3 to 57.5%, 4 to 55%, 5 to 50%, particularly 10 to 47. % Is preferred. If the B ₂ O ₃ content is too large, the refractive index tends to decrease. Further, weather resistance and chemical durability are likely to be lowered.

The content of SiO ₂ is 0 to 66.5%, 0.1 to 66.5%, 1 to 60%, 3 to 57.5%, 4 to 55%, 5 to 50%, particularly 10 to 47%. Preferably there is. When the content of SiO ₂ is too large, the refractive index tends to decrease. Further, striae and bubbles due to undissolved may remain in the glass, and the required quality as an optical lens may not be satisfied.

  In addition to the above components, the glass constituting the present invention may contain the following components.

  ZnO is a component that acts as a flux. Moreover, there exists an effect which improves a weather resistance or stabilizes vitrification. The content of ZnO is preferably 0 to 50%, 0 to 30%, 0 to 10%, 0.1 to 5%, particularly preferably 0.2 to 1%. When there is too much content of ZnO, it will become easy to devitrify and light transmittance will fall easily.

In addition, when the content of P ₂ O ₅ + SnO + TiO ₂ + B ₂ O ₃ + ZnO is 50% or more, 60% or more, particularly 70% or more, the devitrification resistance, weather resistance, and chemical durability are excellent, and It becomes easy to obtain a glass excellent in light transmittance in the visible region or near ultraviolet region. The upper limit of the content of P ₂ O ₅ + SnO + TiO ₂ + B ₂ O ₃ + ZnO is not particularly limited, and may be 100%. However, when other components are contained, it is 99% or less, and further 98% or less. May be. “P ₂ O ₅ + SnO + TiO ₂ + B ₂ O ₃ + ZnO” means the total content of P ₂ O ₅ , SnO, TiO ₂ , B ₂ O ₃ and ZnO.

Al ₂ O ₃ is a component that can form a glass skeleton together with SiO ₂ and B ₂ O ₃ . Moreover, there exists an effect which improves a weather resistance. The content of Al ₂ O ₃ is preferably 0 to 10%, particularly preferably 0.1 to 5%. When the content of Al ₂ O ₃ is too large, it tends to be devitrified. Moreover, there exists a tendency for a meltability to fall or for a light transmittance to fall.

ZrO ₂ is a component that improves weather resistance. However, when there is too much the content, devitrification resistance falls or a melting temperature rises and it becomes easy to fall light transmittance. Therefore, the content of ZrO ₂ is preferably 0 to 2%, 0 to 1.5%, 0.1 to 1%, particularly preferably 0.2 to 0.5%.

La ₂ O ₃ , Gd ₂ O ₃ , Ta ₂ O ₅ , WO ₃ , Nb ₂ O ₅ , Y ₂ O ₃ , Yb ₂ O ₃ and GeO ₂ are components that enhance weather resistance and chemical durability. Moreover, a refractive index can be adjusted by containing these components. The content of La ₂ O ₃ + Gd ₂ O ₃ + Ta ₂ O ₅ + WO ₃ + Nb ₂ O ₅ + Y ₂ O ₃ + Yb ₂ O ₃ + GeO ₂ is 0 to 30%, 0.1 to 20%, 0.3 to 15% 0.5 to 10%, preferably 1 to 7.5%. When there is too much content of these components, it will become easy to produce malfunctions, such as a fall of devitrification resistance, a raise of melting temperature, or a fall of the light transmittance. Note that “La ₂ O ₃ + Gd ₂ O ₃ + Ta ₂ O ₅ + WO ₃ + Nb ₂ O ₅ + Y ₂ O ₃ + Yb ₂ O ₃ + GeO ₂ ” means La ₂ O ₃ , Gd ₂ O ₃ , Ta ₂ O ₅ , WO ₃ , means the total content of Nb ₂ O ₅ , Y ₂ O ₃ , Yb ₂ O ₃ and GeO ₂ .

  MgO, CaO, SrO and BaO (alkaline earth metal oxide) are components that act as fluxes. Moreover, there exists an effect which improves a weather resistance. However, when there is too much content of these components, liquidus temperature will rise (liquidus viscosity will fall) and it will become easy to precipitate a devitrified substance during a melting or a shaping | molding process. In view of the above, the content of MgO + CaO + SrO + BaO is preferably 0 to 30%, 0.5 to 25%, 1 to 20%, and particularly preferably 2 to 15%. “MgO + CaO + SrO + BaO” means the total content of MgO, CaO, SrO and BaO.

Li ₂ O, Na ₂ O and K ₂ O are components that lower the glass transition point. The content of Li ₂ O + Na ₂ O + K ₂ O is preferably 0 to 10%, particularly preferably 0 to 8%. When _{Li 2 O + Na 2 O +} K 2 O content is too large, easily devitrified, chemical durability tends to decrease. In addition, the light transmittance tends to decrease. “Li ₂ O + Na ₂ O + K ₂ O” means the total content of Li ₂ O, Na ₂ O and K ₂ O.

As a fining agent, Cl, S or Br may be contained. The Cl + S + Br content is preferably 0 to 1%, 0.01 to 1%, particularly preferably 0.05 to 0.5%. When there is too much content of Cl + S + Br, it will volatilize at the time of fusion | melting and a melting container will become easy to corrode. “Cl + S + Br” means the total content of Cl, S and Br. Further, as another refining agent, it may contain _Sb 2 _{O 3} or SnO _2. The contents of Sb ₂ O ₃ and SnO ₂ are preferably 0 to 1%, 0.01 to 1%, particularly 0.05 to 0.5%, respectively. If sb ₂ O _3, SnO ₂ content is too large, the light transmittance tends to decrease.

Fe ₂ O ₃ , NiO and CoO are components that reduce the light transmittance. Therefore, it is preferable that these components are not substantially contained (specifically, each is less than 0.1%).

  Since rare earth components such as Ce, Pr, Nd, Eu, Tb and Er may also reduce the light transmittance, the content of these components is preferably less than 1% in terms of oxide.

  Since In and Ga may reduce the light transmittance and are expensive, it is preferably not substantially contained (specifically, less than 0.1% each in terms of oxide).

For environmental reasons, it is preferable that the lead component (for example, PbO) and the arsenic component (for example, As ₂ O ₃ ) are not substantially contained (specifically, less than 0.1% each).

  Next, a method for producing the optical lens for encoder of the present invention will be described. First, a glass raw material having a desired composition and prepared so as to be a glass having a refractive index of 1.65 or more is heated and melted to obtain a glass melt. The melting atmosphere is preferably an inert atmosphere. The inert atmosphere may be a nitrogen, argon or helium atmosphere, but a nitrogen atmosphere is particularly preferred because it is inexpensive. When melted without controlling the atmosphere, that is, when melted in the air, the glass tends to be oxidized and blisters are generated. The melting temperature is preferably 800 to 1200 ° C, particularly 900 to 1100 ° C. When the melting temperature is high, coloring is increased due to impurities eluted from the melting container, and it is difficult to obtain a transparent glass. When the melting temperature is low, the glass raw material is not sufficiently melted, so that undissolved spots are easily generated. As the melting container, refractory, quartz glass, platinum, gold, glassy carbon, or the like can be used.

  Next, molten glass is dropped from the tip of the nozzle to produce droplet glass, and preform glass is obtained. Alternatively, a molten glass is rapidly cast and a glass block is once produced, then ground, polished and washed to obtain a preform glass. In addition, as a material of a nozzle, the thing similar to a melting container can be used. In addition, if the wettability of the glass with respect to the nozzle is high, forming striae easily occur. A gold nozzle is preferable because it has low wettability of glass and can suppress formation of forming striae.

  Subsequently, the preform glass is put into a precision-worked mold and is pressure-formed while being heated until it becomes softened, and the surface shape of the mold is transferred to the preform glass. In this way, an encoder optical lens can be obtained.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these Examples.

Example 1
The glass melt was prepared by blending the raw materials to be SnO 72% and P ₂ O ₅ 28% in a mol%, and melting at 700 to 1000 ° C. for 1 hour using a gold container in a nitrogen atmosphere. Got. Next, a glass melt was dropped into a mold from a gold nozzle to obtain a preform glass. Preform glass is put into a precision-processed mold and pressed while being heated at the softening point. The surface shape of the mold is transferred to the preform glass, and a flat surface with a front curvature radius of 20 mm and a height of 4 mm is used. A convex lens was obtained. Thereafter, the focal length, refractive index, glass transition point, and thermal expansion coefficient of the obtained optical glass lens were evaluated. The obtained optical glass lens had a large refractive index of 1.847 and a focal length of 23.6 mm. Moreover, the glass transition point was 220 degreeC and the thermal expansion coefficient (30-200 degreeC) was 145x10 < ^-7 > / degreeC.

(Example 2)
By the same method as in Example 1, a plano-convex lens having a front curvature radius of 10 mm and a height of 0.5 mm was obtained. The focal length of the obtained optical lens was 12.0 mm. The refractive index, glass transition point, and thermal expansion coefficient were the same as in Example 1.

(Example 3)
In the same manner as in Example 1, a biconvex lens having a front curvature radius of 10 mm, a rear curvature radius of 10 mm, and a height of 0.5 mm was obtained. The focal length of the obtained optical lens was 6.1 mm. The refractive index, glass transition point, and thermal expansion coefficient were the same as in Example 1.

(Comparative example)
The focal length, refractive index, glass transition point, and thermal expansion coefficient of a plano-convex lens of polymethyl methacrylate resin (both front radius of curvature and height are the same as in Example 1) were evaluated. The refractive index was 1.60, which was smaller than that of Example 1, and the focal length was 33.3 mm, which was larger than that of Example 1. When the focal length becomes long, it is difficult to reduce the size of the encoder. The glass transition point was 90 ° C., which was lower than that in Example 1. Therefore, it is likely to be deformed at high temperatures, and the focal length is likely to change. The thermal expansion coefficient (30 to 200 ° C.) was 600 × 10 ⁻⁷ / ° C., which was higher than that in Example 1. Therefore, it is considered that the deformation due to the temperature change becomes large and the focal length is likely to change.

  The focal length was measured using a focal length measuring device.

  The refractive index is indicated by a measured value with respect to d-line (587.6 nm) of a helium lamp.

  As the glass transition point, the value of the first inflection point was adopted in a chart obtained by measuring up to 1000 ° C. using a macro type differential thermal analyzer.

  The thermal expansion coefficient was measured in the range of 30 to 200 ° C. using DILATO METER.

DESCRIPTION OF SYMBOLS 1 Light emitting diode 2 Optical lens 3 Rotating mechanism 4 Rotating shaft 5 Rotating disk 5a Light transmission part 5b Light blocking part 6 Light receiver H Height W Width

Claims (8)

  An optical lens for an encoder, comprising a glass having a refractive index of 1.65 or more and a height of 5 mm or less. Encoder optical lens according to claim 1, characterized in that it consists of SnO-P ₂ O ₅ based glass. A composition, in mol%, SnO _33.5-90%, to claim 1 or 2, characterized in that it consists of glass containing _{2 O 3 0.1~66.5% P 2 O} 5 + SiO 2 + B The optical lens for encoder as described.   The optical lens for an encoder according to any one of claims 1 to 3, wherein the glass transition point is made of glass having a temperature of 200 ° C or higher. The optical lens for an encoder according to any one of claims 1 to 4, wherein the optical lens is made of glass having a thermal expansion coefficient of 200 x ^10-7 / ° C or less in a range of 30 to 200 ° C.   The optical lens for an encoder according to any one of claims 1 to 5, wherein the optical lens is made of glass having a Young's modulus of 60 GPa or less. The optical lens for an encoder according to claim 1, wherein the optical lens is made of glass having a photoelastic constant of 2 × 10 ⁻¹² / Pa or less. The optical lens for an encoder according to any one of claims 1 to 7, wherein an antireflection film is provided on the lens surface.