JP2016031266A - Optical encoder and method for manufacturing optical encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical encoder having high reliability and high accuracy of detecting a temperature change and manufacturable at a low cost.SOLUTION: An optical encoder 100, designed to detect the rotation of a shaft 10 rotating within a certain range of angles, comprises a hub 20 having a seat part 22 extending in the radial direction from a body part 21, a grating plate 30 bonded to the seat part 22 via an elastic adhesive layer, and an optical system for irradiating the grating plate 30 with light and also receiving and detecting the reflected light. The seat part 22 of the hub 20 has an adhesive surface 24 where the elastic adhesive layer is provided, and protruding parts 25 for supporting the grating plate 30 at three or more points and provided at the outer circumference of the adhesive surface 24. The height Hof the protruding parts 25 is a value with which the tensile and shearing stresses acting on the elastic adhesive layer are smaller than previously measured tensile and shearing adhesive strengths, respectively.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical encoder used in a high-speed positioning motor system such as a galvano scanner, and a manufacturing method thereof.

  In recent years, galvano scanner applied products such as laser processing machines are increasingly required to improve processing efficiency, and galvano scanners are also required to have a high-speed response. In a servo system such as a galvano scanner, an optical encoder is used to detect a rotation angle (rotation position) of a motor.

  For example, in the optical encoder disclosed in Patent Document 1, a concave portion is provided on the top surface of the rotating shaft, and a disk having an optical pattern is bonded to the rotating shaft through an adhesive provided in the concave portion. . A groove is formed on the peripheral surface of the recess.

  On the other hand, Patent Document 2 discloses a position measuring device including a glass scale and a fixing jig thereof. Between the glass scale and the fixing jig, there is an elastic layer formed by a preheated adhesive, and thermal stress caused by the difference in linear expansion coefficient between the glass scale and the fixing jig Is absorbed by the bending of the elastic layer.

Japanese Patent Publication No. 08-012086 (see FIGS. 2A and 2B) Japanese Patent No. 4477440 (see FIG. 2)

  According to the optical encoder disclosed in Patent Document 1, the adhesive can be released from the groove formed on the peripheral surface of the recess, which is effective. However, this structure does not take into account the thermal stress caused by the difference in linear expansion coefficient between the disk, the adhesive layer, and the rotating shaft. When the environmental temperature changes greatly, for example, when the environmental temperature drops significantly during transportation, excessive thermal stress acts and peeling occurs between the disk and the rotating shaft, which is a problem in terms of reliability against temperature changes. Occurs.

  On the other hand, according to the bonding method disclosed in Patent Document 2, although the thermal stress is certainly relieved, there is a problem that the bonding process is complicated and the manufacturing cost increases.

  In general, optical encoders are required to have high detection accuracy.

  An object of the present invention is to provide an optical encoder that has high reliability and high detection accuracy with respect to a temperature change and can be manufactured at low cost, and a manufacturing method thereof.

In order to achieve the above object, the present invention relates to an optical encoder that detects the rotation of a rotating body that rotates within a certain angular range.
This optical encoder includes a hollow main body and a hub having a seat extending in the radial direction from the main body, a grating plate bonded to the seat via an elastic adhesive layer, and the grating plate. A light projecting unit that emits light and a light receiving unit that receives light from the grating plate. The seat portion of the hub includes an adhesive surface provided with an elastic adhesive layer, and one or a plurality of protrusions provided on the outer peripheral portion of the adhesive surface to support the grating plate at three or more points. Have.

  The optical encoder includes, for example, a step of applying an elastic adhesive on the bonding surface, a step of pressing a grating plate against the protrusion, and a step of curing the elastic adhesive to form an elastic adhesive layer. It is manufactured by the method containing.

  Preferably, the thickness of the elastic adhesive layer at the adhesive curing temperature is such that the tensile stress and shear stress acting between the elastic adhesive layer and the grating plate are measured in advance. It is a value within a range smaller than each.

According to the present invention, when the grating plate is bonded to the seat portion of the hub, the projection portion supports the grating plate, and the gap between the optical system (light projecting portion and light receiving portion) and the grating plate is made uniform. To do. Thereby, generation | occurrence | production of the detection error according to the position at the time of rotation is prevented.
In the adhesive structure of the present invention, the thickness of the elastic adhesive layer is defined by the height of the protrusion. The thermal stress (tensile stress, shear stress) acting between the grating plate and the elastic adhesive layer is absorbed and reduced by the deformation of the elastic adhesive layer, and the height of the protrusion should be set within a suitable range. Thus, peeling of the grating plate can be easily and reliably prevented.
Further, the bonding structure and bonding process in this optical encoder are very simple compared to the conventional one.

  As described above, an optical encoder that has high reliability with respect to temperature change and high detection accuracy and can be manufactured at low cost and a manufacturing method thereof are realized.

It is an optical encoder which concerns on Embodiment 1 of this invention, Comprising: It is a perspective view which shows the state before adhesion | attachment of a grating plate. It is a side view which shows an optical encoder. It is a top view which shows the structure of a grating board, (a) shows a rotating disk, (b) shows the grating board which cut out a part of rotation angle from the rotating disk. It is a top view which shows the example of arrangement | positioning of the protrusion part of the hub in Embodiment 1 of this invention, (a) is provided with four protrusion parts, (b) is provided with three protrusion parts. It is a figure for demonstrating the tensile stress which acts on an adhesive bond layer, (a) shows the periphery part of the adhesive bond layer in adhesive hardening temperature, (b) is the adhesive layer of an adhesive layer in low temperature environment temperature The peripheral part is shown. It is a graph which shows the relationship between the thermal stress which acts on an adhesive bond layer, and the height (thickness of an adhesive bond layer) of a projection part. It is a top view which shows the example of arrangement | positioning of the protrusion part of the hub in Embodiment 2 of this invention, (a) is a wall-shaped protrusion part which covers a part of outer peripheral part of an adhesion surface, (b) is an adhesion surface. A wall-shaped protrusion that covers the entire outer periphery is provided.

  Hereinafter, an optical encoder according to an embodiment of the present invention will be described with reference to the drawings. In each figure, the same or similar components are denoted by the same reference numerals. Further, the terms “upper” and “lower” indicating the direction are for the purpose of specifying the direction in the drawing, and do not limit the installation direction of the apparatus.

Embodiment 1 FIG.
FIG. 1 is a perspective view showing the optical encoder according to the first embodiment of the present invention before the grating plate 30 is bonded. FIG. 2 is a side view showing the optical encoder.
Optical encoder 100 (hereinafter simply referred to as encoder 100) detects the rotation (rotation angle, rotation direction) of shaft 10. The encoder 100 includes a hub 20 for fixing the grating plate 30 to the shaft 10, a grating plate 30 having an optical pattern 31 formed on the surface, an elastic adhesive layer 40 (hereinafter simply referred to as an adhesive layer 40), light projection Unit 50 and light receiving unit 60.

  The shaft 10 is an example of a rotating body that rotates within a certain angle range, and is a shaft of a servo motor, for example. The shaft 10 may rotate in one direction or may rotate (swing) in both directions.

  The hub 20 is made of aluminum, stainless steel, or the like. The hub 20 includes a hollow main body 21 that is inserted into and fixed to the shaft 10, and a main body 21 in a radial direction (Y-axis direction) perpendicular to the rotation axis of the shaft 10 (indicated by a dashed line in FIG. 1). And a seat portion 22 extending from the head. The seat 22 includes a bottom surface 23, a flat adhesive surface 24, a plurality of protrusions 25 provided on the adhesive surface 24, and positioning reference surfaces 26 and 27. The bonding surface 24 is located above the bottom surface 23 through a step.

  There are three or more protrusions 25, and the grating plate 30 is supported at three or more points. As will be described later, since the thermal stress (tensile stress) decreases as the distance between the plurality of protrusions 25 increases, the protrusion 25 is not disposed at the center of the bonding surface 24, and the outer periphery of the bonding surface 24 is not disposed. It is preferable to arrange the protrusion 25. The adhesive layer 40 is present on a portion of the adhesive surface 24 where the protrusions 25 are not provided. The lower surface of the grating plate 30 and the seat portion 22 are bonded via the adhesive layer 40. Further, the protrusion 25 has a height equal to the thickness of the adhesive layer 40 and is in contact with and supports the grating plate 30. The positioning reference surfaces 26 and 27 of the seat portion 22 are erected in a direction perpendicular to the bonding surface 24. Therefore, in FIG. 1, the positioning reference surface 26 is parallel to the YZ plane, and the positioning reference surface 27 is parallel to the XZ plane. Positioning of the grating plate 30 in the seat portion 22 in the X-axis direction, the Y-axis direction, and the Z-axis direction is performed by the positioning reference surface 26, the positioning reference surface 27, and the protrusion 25, respectively.

  Examples of the adhesive (elastic adhesive) constituting the adhesive layer 40 are a silicon adhesive, a urethane adhesive, an acrylic adhesive, and the like. In particular, from the viewpoint of alleviating thermal stress, a urethane-based adhesive having a Young's modulus of 700 [MPa] or less at normal temperature is preferable. By using this urethane-based adhesive, the grating plate 30 at the central portion of the bonding surface 24 is used. Can be prevented.

  The light projecting unit 50 is a laser diode, LED (light emitting diode), or the like, and irradiates the grating plate 30 with light. The light receiving unit 60 is a light receiving element such as a photodiode, and receives light reflected from the grating plate 30 and performs photoelectric conversion. The light projecting unit 50 and the light receiving unit 60 are disposed on the same side of the surface of the grating plate 30 with a predetermined gap from the surface. That is, the encoder 100 is a so-called reflective optical encoder.

Next, the structure of the grating plate 30 will be described with reference to FIG.
FIG. 3A shows a rotating disk. The rotating disk is a donut disk of 360 degrees around the shaft 10 and has a hole (shaft hole) 32 through which the shaft 10 passes in the center. FIG. 3B shows the grating plate 30 obtained by cutting out a part of the rotation angle from the rotating disk shown in FIG. The grating plate 30 has a structure without a shaft hole, and its thickness is small and uniform. The shape of the illustrated grating plate 30 is rectangular, but other shapes may be used depending on the configuration of the seat portion 22, for example, a circular plate without a shaft hole.

  On the surface of the grating plate 30, optical patterns 31 are provided radially at predetermined intervals within a certain angular range. The grating plate 30 may be a glass plate. The optical pattern 31 is formed by depositing a metal thin film such as aluminum. A dielectric multilayer film may be deposited instead of aluminum or the like.

Next, the example of arrangement | positioning of the projection part 25 in the hub 20 is demonstrated using FIG.
As shown in FIG. 4, the adhesive surface 24 of the hub 20 has a shape close to a rectangle, but one of the four sides of the rectangle that is far from the rotation center of the shaft 10 in the Y-axis direction is slightly curved. Yes. In FIG. 4A, protrusions 25 a to 25 d are provided at four locations on the outer peripheral portion of the bonding surface 24. The protrusions 25a and 25b are provided at both corners of the curved side, and the protrusions 25c and 25d are provided at both corners of the side facing the curved side. In FIG. 4B, projections 25 a, 25 b, and 25 e are provided at three locations on the outer peripheral portion of the bonding surface 24. The protrusions 25a and 25b are the same as in FIG. 4A, and the protrusion 25e is provided at the center of the side facing the curved side.

  According to the arrangement example of the protrusions 25 in the first embodiment, the protrusions 25 are not connected to each other and do not constitute a wall, so that excess adhesive easily flows from the adhesive surface 24 to the bottom surface 23. The thickness of the adhesive layer 40 can be made more uniform. Further, since the adhesive easily flows out of the bonding surface 24, the pressing load on the grating plate 30 during bonding can be reduced. Further, since the plurality of protrusions 25 are not connected to each other, the bonding area between the grating plate 30 and the adhesive layer 40 can be increased to improve the bonding strength.

Next, the operation of the encoder 100 will be briefly described.
The light emitted from the light projecting unit 50 is applied to the optical pattern 31 on the surface of the grating plate 30 and reflected. The reflected light is received by the light receiving unit 60 and detected as an electrical signal. At this time, when the shaft 10 is rotated and the hub 20 and the grating plate 30 are rotated accordingly, the amount of light detected by reaching the light receiving unit 60 is periodically changed, and thus the electric signal is also periodically changed. It will be. Therefore, the rotation angle of the shaft 10 can be detected by measuring the change of the electric signal.

Next, steps S1 to S4 included in the method for manufacturing the encoder 100 will be briefly described.
(S1) An adhesive is applied to the adhesive surface 24.
(S2) With the end face of the grating plate 30 pressed against the positioning reference surfaces 26 and 27, the grating plate 30 is pressed against the projection plate 25 from the upper side, and the grating plate 30 is pressed against the protrusion 25. As a result, the seat portion 22 of the hub 20 and the grating plate 30 are bonded.
(S3) The adhesive layer 40 is formed by curing the adhesive.
(S4) The main body 21 of the hub 20 is press-fitted into the shaft 10.

  In step S <b> 2, the grating plate 30 is pressed against the positioning reference surfaces 26 and 27 to be positioned in the X-axis direction and the Y-axis direction, and is positioned in the Z-axis direction by being supported on the protrusion 25. Thereby, after process S3, the thickness of the adhesive bond layer 40 corresponds with the height of the projection part 25. In other words, the thickness of the adhesive layer 40 is defined by the height of the protrusion 25. In step S <b> 2, excess adhesive moves from the adhesive surface 24 to the bottom surface 23 through the gap between the protrusions 25.

  Here, the accuracy of the gap between the optical system (the light projecting unit 50 and the light receiving unit 60) and the grating plate 30 depends on the positioning accuracy of the grating plate 30 with respect to the seat portion 22 in the Z-axis direction. If the grating plate 30 is bonded to the seat portion 22 while being tilted from the Z-axis direction, the surface of the grating plate 30 on which the optical pattern 31 is formed does not become exactly perpendicular to the axial direction of the shaft 10. Therefore, the gap between the optical system and the optical pattern 31 varies according to the position at the time of rotation, and a detection error occurs.

  In the first embodiment, the bonding is performed in a state in which the protruding portion 25 supports the grating plate 30, and the excessive adhesive escapes out of the bonding surface 24. Therefore, the rotation axis direction (Z-axis direction) of the shaft 10 and the surface of the grating plate 30 are accurately orthogonal to each other. As a result, the gap between the optical system and the grating plate 30 becomes uniform over the entire surface of the grating plate 30, and detection errors corresponding to the position during rotation are prevented.

  In the method described above, steps S1 to S3 are performed before the step S4, but may be performed after the step. That is, the grating plate 30 may be bonded to the hub 20 after the main body 21 is press-fitted into the shaft 10.

  Next, thermal stress acting between the grating plate 30 and the adhesive layer 40 will be examined.

  The environmental temperature of the encoder 100 may decrease to about minus several tens of degrees during transportation or the like, while it may increase to about 80 degrees due to heat generated from the motor. When the environmental temperature changes from the adhesive curing temperature (typically 25 degrees) to such a low temperature environment temperature or a high temperature environment temperature, it is caused by a difference in linear expansion coefficients of the hub 20, the adhesive layer 40, and the grating plate 30. Thermal stress is generated.

  The bonding area between the adhesive layer 40 and the hub 20 is larger than the bonding area between the adhesive layer 40 and the grating plate 30. Therefore, peeling caused by thermal stress at the interface between the adhesive layer 40 having a smaller contact area and the grating plate 30 becomes a problem. Here, in general, thermal stress is expressed by tensile stress (or compressive stress) and shear stress.

  When the thickness of the adhesive layer 40 is large, it is considered that the tensile stress (compressive stress) acting on the adhesive layer 40 is increased and tensile peeling occurs. The adhesive layer 40 expands in the Z-axis direction at high temperatures and contracts in the Z-axis direction at low temperatures. Since the grating plate 30 is not constrained in the Z-axis direction, it can be freely deformed against the expansion of the adhesive layer 40 at a high temperature. On the other hand, with respect to the shrinkage of the adhesive layer 40 at a low temperature, since the end of the grating plate 30 is supported by the protrusions 25, a force (tensile stress) that causes the adhesive layer 40 to pull the grating plate 30 is generated. That is, according to the first embodiment, the peeling due to the compressive stress acting at the high temperature environment temperature does not cause a problem. Therefore, in the following, only the peeling due to the tensile stress acting at the low-temperature environment temperature will be considered.

  On the other hand, when the thickness of the adhesive layer 40 is small, it is considered that the shear stress acting on the adhesive layer 40 increases and shear peeling occurs. Since the longitudinal elastic modulus (Young's modulus) of the adhesive layer 40 is smaller than that of the hub 20 and the grating 30, the adhesive layer 40 is deformed. Due to the deformation of the adhesive layer 40, the shear stress is relieved.

  In summary, it is considered that tensile peeling and shear peeling at the interface between the grating plate 30 and the adhesive layer 40 are prevented by setting the thickness of the adhesive layer 40 within a suitable range. As described above, the thickness of the adhesive layer 40 matches the height of the protrusion 25.

The inventors noticed that the peeling of the adherend was caused by thermal stress (tensile stress, shear stress) generated at the interface between the grating plate 30 and the adhesive layer 40. Further, as explained, it has been found that the tensile stress is relaxed by the bending of the grating plate 30 under the low temperature environment temperature. Furthermore, since the amount of bending is very small, it has been found that the gap accuracy is not affected.
Hereinafter, a suitable range of the height of the protrusion 25 will be examined in detail by dividing into tensile stress and shear stress.

First, symbols are defined as follows.
ΔT [° C.]: Difference between adhesive curing temperature and low temperature environment temperature H ₀ [mm]: Height of protrusion 25 (length in the Z-axis direction)
Α _m [1 / ° C.] Coefficient of linear expansion of the hub 20 L _0A [mm]: Maximum distance in the bonding area L _0T [mm]: Minimum distance between the protrusions 25 L _0TV [mm]: Distance Distance in the linear adhesion region perpendicular to _L0T , H _g [mm]: Thickness of the grating plate 30 (length in the Z-axis direction)
E _g [MPa]: Longitudinal elastic modulus of the grating plate 30 α _g [1 / ° C.] Linear expansion coefficient of the grating plate 30 I _g [mm ⁴ ]: Sectional moment of inertia of the grating plate 30 A ₀ [ mm ² ]: Adhesive area between the adhesive layer 40 and the lower surface of the grating plate 30 • E _a [MPa]: Longitudinal elastic modulus of the adhesive layer 40 • G _a [MPa]: Transverse elastic coefficient of the adhesive layer 40 • α _a [1 / ° C.]: Linear expansion coefficient of the adhesive layer 40

1. Tensile stress Since the end portion of the grating plate 30 is supported by the protrusions 25 against the shrinkage of the adhesive layer 40 at the low-temperature environment temperature, the force (tensile stress) that the adhesive layer 40 pulls the grating plate 30. ) Occurs. When the thickness of the adhesive layer 40 is large and the thickness of the grating plate 30 is sufficiently thin, the tensile stress is relieved by the bending of the grating plate 30. At this time, since the amount of bending of the grating plate 30 is very small, it does not affect the accuracy of the gap. In other words, the gap varies between the optical system and the grating plate 30 according to the position during rotation due to the deflection of the grating plate 30, and this variation is at a level that does not cause a problem for detection accuracy. .

FIG. 5 is a diagram for explaining the tensile stress acting on the adhesive layer.
FIG. 5A shows the periphery of the adhesive layer 40 at the adhesive curing temperature. The adhesive curing temperature is a temperature at which the adhesive is cured in step S3. At the adhesive curing temperature, the thickness of the adhesive layer 40 is equal to the height of the protrusion 25 (the length in the Z-axis direction) and is H ₀ [mm].
FIG.5 (b) shows the peripheral part of the adhesive bond layer 40 in low temperature side environmental temperature. At the low ambient temperature, the height of the protrusion 25 contracts to H _m [mm], and the thickness of the adhesive layer 40 contracts to H _a1 [mm]. Actually, since the grating plate 30 is bonded to the adhesive layer 40, the grating plate 30 is pulled by the adhesive layer 40 and bent. The thickness of the adhesive layer 40 at the most bent portion (the center portion in the first embodiment) is indicated by H _a [mm]. H _m [mm] and H _a1 [mm] are represented by formula (1) and formula (2), respectively.

Hereinafter, the balance of the tensile stress at the interface between the grating plate 30 and the adhesive layer 40 is simply modeled by the both end support beams to which the equally distributed load is applied.
It is assumed that both ends of the length (length in the Y-axis direction) L _0T [mm] of the adhesive surface 24 are supported, and an _evenly distributed tensile load w [N / mm] acts on the adhesive layer 40. When the elongation (Z-axis direction) of the adhesive layer 40 after shrinkage is ΔH _a [mm], the relationship among H _a , H _a1 , and ΔH _a is expressed by Expression (3).

The balance of the tensile stress at the interface between the grating plate 30 and the adhesive layer 40 is shown in Equation (4). In Equation (4), W [N] is a total load applied to the adhesive layer 40, and is represented by W [N] = w [N / mm] × L _0T [mm]. L _0T [mm] is a length L _0m [mm] between the support portions 25 when contracted at the low temperature environment temperature. When L _0m [mm] is about several tens of millimeters or less, the contraction amount of L _0m [mm] is very small, so that there is no problem in approximating L _0T [mm] with L _0m [mm]. The width (length in the X-axis direction) of the grating plate 30 is L _0TV [mm]. Similar to L _0T [mm], the amount of shrinkage at the low-temperature environment temperature is very small, so there is no problem in approximating the length before shrinkage. A ₀ [mm ² ] is an area of the bonding surface, and is represented by A ₀ [mm ² ] = L _0T [mm] × L _0TV [mm]. Similarly, since the amount of shrinkage of the A ₀ [mm ² ] at the low-temperature environment temperature is small, there is no problem in approximating the area before shrinkage.

In this model, generally, the maximum amount of deflection (Z-axis direction) of the grating plate 30 is δ [mm], and the equally distributed tensile load w [N / mm] is expressed by Equation (5). However, the maximum amount of deflection δ [mm] is expressed by Expression (6), and the secondary moment of inertia I _g [mm ⁴ ] of the grating plate 30 is expressed by Expression (7).

Substituting Equation (5) and Equation (6) into Equation (4) and solving for ΔH _a [mm] yields Equation (8). However, _{K 1} in the formula (8) is expressed by Equation (9).

  The tensile stress σ [MPa] acting on the adhesive layer 40 is expressed by the equation (10) from Hooke's law.

As can be seen from equation (10), a tensile stress acts on the adhesive layer 40 sigma [MPa] is represented by the height H ₀ function [mm] of the protrusion 25, large enough to H ₀ [mm] is increased Become. Note that it can also be seen from the equation (10) that the tensile stress σ decreases as the distance L _0T [mm] between the protrusions 25 increases.

In order to prevent the grating plate 30 from being peeled off from the adhesive layer 40, the tensile stress σ [MPa] is subjected to a condition that is smaller than the tensile adhesive strength σ _c [MPa] (σ <σ _c ). The tensile bond strength σ _c is a value that can be measured, for example, according to JIS K6849 (1994). By substituting equation (10) into this condition (σ <σ _c ), inequality (11) for H _g is obtained. Equation (11) is transformed to give inequality (12) for H ₀ . However, equation (11), _{K 2} in the formula (12) is expressed by Equation (13).

When the thickness H _g [mm] of the grating plate 30 satisfies the expression (11) or the height H ₀ [mm] of the protrusion 25 satisfies the expression (12), the grating is caused by the tensile stress. The plate 30 is not peeled off from the adhesive layer 40.

Incidentally, formula (12), when the right side of equation (13) becomes minimum _is, H g _[mm], the most severe condition for H 0 [mm]. Therefore, as described above, L _0T [mm] is defined as “minimum distance between the protrusions 25”, and L _0TV [mm] is defined as “distance within the linear adhesion region perpendicular to the distance L _0T ”. ing.

2. Shear stress When the temperature change ΔT [° C.] occurs, the hub 20 and the grating plate 30 expand or contract, respectively. At the low-temperature environment temperature, the length L ₀ [mm] of the bonding surface 24 shrinks to L _0A [mm], and the length of the portion in contact with the adhesive layer 40 on the back surface of the grating plate 30 (the length in the Y-axis direction). ) Contracts from L ₀ [mm] to L _g [mm]. L _0A [mm] and L _g [mm] are represented by formula (14) and formula (15), respectively.

  Since the longitudinal elastic modulus of the adhesive layer 40 is smaller than the longitudinal elastic modulus of the hub 20 and the grating 30, the adhesive layer 40 is deformed. The deformation amount λ [mm] in the Y-axis direction of the adhesive layer 40 is expressed by Expression (16).

  The shear stress τ [MPa] due to the elongation (shrinkage) of the adherend due to the temperature change is expressed by the equation (17) by substituting the equation (16) into the Hooke's law.

As can be seen from equation (16), the shear stress acting on the adhesive layer 40 tau [MPa] is represented by the height function of the H ₀ [mm] of the protrusion 25, large enough to H ₀ [mm] is reduced Become.
As in the case of tensile stress, the shear stress τ [MPa] is smaller than the shear bond strength τ _c [MPa] (τ <τ _c ) so that the grating plate 30 is not peeled off from the adhesive layer 40. ) Is imposed. The shear bond strength τ _c is a value that can be measured, for example, according to JIS K6850 (1999). By substituting equation (17) into this condition (τ <τ _c ), inequality (18) for H ₀ is obtained.

When the height H ₀ [mm] of the protrusion 25 satisfies the formula (18), the grating plate 30 is not peeled off from the adhesive layer 40 due to shear stress.

Note that the time when the right side of Expression (18) is the smallest is the most severe condition for H ₀ [mm]. Therefore, as described above, L _0A [mm] is defined as “the maximum distance in the adhesion region”.

From the above, when the height H ₀ [mm] of the protrusion 25 satisfies the expressions (12) and (18) simultaneously, that is, when H ₀ [mm] satisfies the expression (19), the thermal stress (tensile stress) The grating plate 30 is not peeled off from the adhesive layer 40 due to shear stress).

(Example)
As an example, the height H ₀ of the protrusion 25 when aluminum is used as the material of the hub 20, glass is used as the material of the grating plate 30, and a urethane-based adhesive is used as the adhesive constituting the adhesive layer 40. The preferred range of [mm] was calculated.

Typical conditions are listed below.
・ Temperature change ΔT [° C.] = 55
The linear expansion coefficient α _m [1 / ° C.] = 2.3 × 10 ^{−5 of the} hub 20
_-Minimum distance L _0T [mm] = 3.0 between the protrusions 25
And distance _{L 0T} a distance _L 0TV in adhesion area of the line vertical [mm] = 4.0
・ Maximum distance L _0A [mm] in the adhesion area = 5.0
The longitudinal elastic modulus E _g [MPa] = 7.1 × 10 ^{4 of the} grating plate 30
The linear expansion coefficient α _g of the grating plate 30 [1 / ° C.] = 8.5 × 10 ⁻⁶
-Adhesion area A ₀ [mm ² ] = 13 between the adhesive layer 40 and the lower surface of the grating plate 30
The longitudinal elastic modulus E _a [MPa] of the adhesive layer 40 = 7.0 × 10 ²
The transverse elastic modulus G _a [MPa] of the adhesive layer 40 = 2.3 × 10 ²
The linear expansion coefficient α _a [1 / ° C.] = 2.5 × 10 ^{−4 of the} adhesive layer 40
・ Tensile bond strength σ _c [MPa] = 7.0
Shear bond strength τ _c [MPa] = 16

By substituting the above value into the equation (18), the height H ₀ [mm]> 5.8 × 10 ^{−2 of} the protrusion 25 is obtained. As an example, when H ₀ [mm] = 6.0 × 10 ⁻² is set and this value is substituted into the equation (11), the thickness H _g [mm] <2.0 of the grating plate 30 is obtained. As an example, H _g [mm] = 1.5. If H _g [mm] ≦ 1.5, it can be said that the grating plate 30 is bent when the tensile stress is applied, and the tensile stress is relaxed.

The tensile stress σ acting on the adhesive layer 40 is calculated based on the equation (10), the shear stress τ acting on the adhesive layer 40 is calculated based on the equation (17), and the height ( A graph was created by plotting as a function of the thickness of the adhesive layer 40. This graph is shown in FIG.
From FIG. 6, it was found that the range of the height H ₀ [mm] of the protrusion 25 where tensile peeling and shear peeling did not occur was about 0.06 [mm] to about 0.15 [mm]. Further, the maximum deflection amount δ calculated based on the formula (6) is less than 1.0 × 10 ⁻³ [mm] and is a negligible value with respect to the accuracy of the gap.

Embodiment 2. FIG.
FIG. 7 is a plan view showing an arrangement example of the protrusions of the hub according to the second embodiment of the present invention.
The second embodiment is different from the first embodiment in the configuration of the protrusion 25. Other configurations of the encoder 100 are the same as those of the first embodiment, and the same reference numerals are given in the drawings, and description thereof is omitted.

  FIG. 7A corresponds to FIG. 4A in which the protrusions 25 a to 25 d are provided at four locations on the outer peripheral portion of the bonding surface 24. Two projections 25a and 25b that are far from the rotation center of the shaft 10 in the Y-axis direction (on the curved side) are connected to each other, and a wall-like projection 25f that covers a part of the outer peripheral portion of the bonding surface 24 is connected. Is formed.

  Here, as the number of gratings increases, the resolution of the encoder can be improved. Therefore, from the viewpoint of improving the resolution, it is preferable that the optical pattern 31 is formed at a position as far as possible in the Y-axis direction when viewed from the rotation center of the shaft 10. At this time, in order to improve the accuracy of the gap between the optical system and the grating plate 30, it is preferable that the wall-shaped protrusion 25f extends over the optical pattern 31 and supports the entire area thereof.

  Here, considering workability, it is desirable that the amount of the adhesive protruding from the seat portion 22 is as small as possible. In the second embodiment, the wall-shaped protrusion 25f makes it difficult for the adhesive to flow toward the curved side, and the workability can be improved by reducing the amount of the adhesive protruding from the seat portion 22.

  In FIG. 7B, a wall-like protrusion 25 g that covers the entire outer peripheral portion of the bonding surface 24 is provided. The structure of the protrusion 25g is very simple and can be manufactured at low cost because it is easy to process. 7B, the accuracy of the gap between the optical system and the grating plate 30 can be improved as in FIG. 7A.

  The present invention has been described with reference to the above embodiment, but the present invention is not limited to this embodiment, and various modifications and improvements may be added to the above embodiment.

  For example, although the reflection type optical encoder has been described in the above embodiment, the present invention is not limited to this, and the light projecting unit 50 and the light receiving unit 60 are located on the opposite sides of the grating plate 30. It may be a type optical encoder. In this case, the grating plate 30 has a shape such that the optical pattern 31 protrudes outward from the outer peripheral portion of the bonding surface 24, or is arranged in such a manner. As a result, the seat portion 22 does not exist on the lower surface side of the optical pattern 31. In addition, the light projecting unit 50 and the light receiving unit 60 are disposed on the opposite sides with respect to the surface of the grating plate 30. Thereby, the light emitted from the light projecting unit 50 passes through the optical pattern and is detected by the light receiving unit 60.

DESCRIPTION OF SYMBOLS 10 Shaft, 20 Hub, 21 Body part, 22 Seat part, 23 Bottom face, 24 Adhesive surface, 25 (25a-25g) Protrusion part, 26,27 Positioning reference surface, 30 Grating plate, 31 Optical pattern, 40 Elastic adhesive layer , 50 Projector, 60 Receiver, 100 Optical encoder

Claims (8)

An optical encoder that detects the rotation of a rotating body that rotates within a certain angular range,
A hub having a hollow body and a seat extending radially from the body;
A grating plate bonded to the seat through an elastic adhesive layer;
A light projecting unit that irradiates light to the grating plate;
A light receiving portion for receiving light from the grating plate,
The seat includes an adhesive surface on which the elastic adhesive layer is provided, and one or a plurality of protrusions provided on an outer peripheral portion of the adhesive surface to support the grating plate at three or more points. An optical encoder characterized by comprising: The one or more protrusions include a wall-like protrusion that covers at least a part of the outer peripheral portion of the bonding surface.
The optical encoder according to claim 1. The adhesive surface is located above the bottom surface of the seat,
The optical encoder according to claim 1 or 2. The elastic adhesive layer is made of a urethane adhesive,
The optical encoder according to any one of claims 1 to 3. The thickness of the grating plate is 1.5 [mm] or less,
The optical encoder according to any one of claims 1 to 4. A method for manufacturing the optical encoder according to claim 1,
Applying an elastic adhesive on the adhesive surface;
Pressing a grating plate against the one or more protrusions;
Curing the elastic adhesive to form an elastic adhesive layer,
The height H ₀ [mm] of the one or more protrusions acts on the elastic adhesive layer that changes according to the difference ΔT [° C.] between the curing temperature of the elastic adhesive and the low-temperature environment temperature. Production of optical encoder, wherein tensile stress and shear stress are values within a range smaller than the previously measured tensile bond strength σ _c [MPa] and shear bond strength τ _c [MPa], respectively. Method. The height H ₀ [mm] of the one or more protrusions is expressed by the following formulas (1) and (2).
The filling,

here,
ΔT [° C.] is the difference between the adhesive curing temperature and the low-temperature environment temperature,
α _m [1 / ° C] is the linear expansion coefficient of the hub,
L _0A [mm] is the maximum distance in the bonded area,
L _0T [mm] is the minimum distance between the protrusions,
L _0TV [mm] is a distance in a straight adhesion region perpendicular to the distance L _0T ,
H _g [mm] is the thickness of the grating plate,
E _g [MPa] is the longitudinal elastic modulus of the grating plate,
α _g [1 / ° C.] is the coefficient of linear expansion of the grating plate,
A ₀ [mm ² ] is an adhesion area between the adhesive layer and the lower surface of the grating plate,
E _a [MPa] is the longitudinal elastic modulus of the adhesive layer,
G _a [MPa] is the transverse elastic modulus of the adhesive layer,
α _a [1 / ° C.] is a linear expansion coefficient of the adhesive layer,
A method for manufacturing the optical encoder according to claim 6. The seat has a positioning reference surface that is erected in a direction perpendicular to the adhesive surface;
In the step of pressing the grating plate against the one or more protrusions, the grating plate is pressed in a state where an end surface of the grating plate is pressed against a positioning reference surface,
A method for manufacturing the optical encoder according to claim 6 or 7.

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