Optical encoder

Abstract

An encoder according to the present disclosure comprises: a reflective member that follows an object to be measured and has a plurality of arranged slits; a plate-shaped member; a light-emitting unit that is disposed on the plate-shaped member; a light-receiving unit that is disposed on the plate-shaped member so as to face the light-emitting unit with the reflective member interposed therebetween; a bonding wire that electrically connects the light-receiving unit to a terminal on the plate-shaped member and has a loop shape protruding toward the reflective member from the light-receiving unit to the terminal; and a light-transmissive protective member that covers the light-emitting unit and the light-receiving unit. The protective member has a height lower than the height from the plate-shaped member to the highest point of the bonding wire.

Description

Optical encoder

[0001] The present disclosure relates to an optical encoder.

[0002] In an optical reflection-type encoder, a technique of covering a light-emitting and receiving element mounted on a substrate with a light-transmissive resin is known in order to protect the light-emitting and receiving element (for example, Patent Document 1). When a configuration in which the light-emitting and receiving element is electrically connected to the substrate by bonding wires is adopted, the bonding wires also need to be covered with a protective member together with the light-emitting and receiving element. Generally, the height from the substrate to the highest point of the bonding wire is higher than the height from the substrate to the surface of the light-emitting and receiving element. Therefore, when the light-emitting and receiving element and the bonding wires are uniformly covered with a protective member having a height that can sufficiently protect the bonding wires, the light-emitting and receiving element will be covered with an unnecessarily thick protective member, which will reduce the light-receiving sensitivity of the light-receiving element and degrade the performance of the encoder.

[0003] Japanese Patent Application Laid-Open No. 2007-3209

[0004] A technique for protecting the substrate and the light-emitting and receiving element mounted on the substrate and suppressing an unnecessary decrease in the light-receiving sensitivity of the light-receiving element is desired.

[0005] The optical encoder according to the present disclosure includes a reflection member having a plurality of arranged slits that is driven by a measurement object, a plate-like member, a light-emitting portion arranged on the plate-like member, a light-receiving portion arranged on the plate-like member so as to face the light-emitting portion via the reflection member, a bonding wire having a loop shape that protrudes from the light-receiving portion toward the reflection member over the terminals on the plate-like member, and a light-transmissive protective member that covers the light-emitting portion and the light-receiving portion. The protective member has a height lower than the height from the plate-like member to the highest point of the bonding wire.

[0006] Figure 1 is a perspective view showing an encoder according to this embodiment. Figure 2 is a cross-sectional view showing the configuration of the encoder in Figure 1. Figure 3 is a diagram showing an example of the optical path of light incident on the light receiving unit in Figure 2. Figure 4 is a cross-sectional view showing the configuration of a conventional encoder. Figure 5 is a diagram showing an example of the optical path of light incident on the light receiving unit in Figure 4. Figure 6 is a cross-sectional view showing the configuration of an encoder according to a first modified example of this embodiment. Figure 7 is a cross-sectional view showing the configuration of an encoder according to a second modified example of this embodiment.

[0007] An encoder according to an embodiment of the present invention is an optical reflective encoder having a substrate on which a light-emitting unit and a light-receiving unit are mounted. The light-receiving unit is electrically connected to terminals (electrodes) provided on the substrate by bonding wires. To protect from the external environment, the light-emitting unit, the light-receiving unit, and the bonding wires are covered with a light-transmitting protective member. One feature of the encoder according to this embodiment is that the height of the protective member covering the light-emitting unit and the light-receiving unit is lower than the height of the bonding wires (the height of the protective member covering the bonding wires). As a result, compared to conventional encoders in which the light-emitting unit, the light-receiving unit, and the bonding wires are covered with a protective member of uniform height that can cover the bonding wires, the following effects are achieved. That is, while protecting the light-emitting unit, the light-receiving unit, and the bonding wires with the protective member as in the conventional case, the angle of incidence of light emitted from the light-emitting surface of the light-emitting unit and incident on the light-receiving surface of the light-receiving unit via the reflective member can be made closer to a direction perpendicular to the light-receiving surface of the light-receiving unit compared to the conventional case. As a result, the light energy density per unit area on the light-receiving surface of the light-receiving unit is improved compared to conventional designs, thereby improving light-receiving sensitivity. This improvement in light-receiving sensitivity can lead to improved detection accuracy by the encoder, improved resolution, and miniaturization while maintaining conventional performance.

[0008] The encoder according to this embodiment will be described below with reference to the drawings. In the following description, components having substantially the same function and configuration will be denoted by the same reference numerals, and redundant explanations will be given only when necessary. In this embodiment, a rotary encoder that detects the rotation angle, rotation speed, and rotation direction of an object to be detected will be described as an example.

[0009] As shown in Figures 1 and 2, the encoder 1 according to this embodiment includes a reflective member 70 (code wheel) 70 that moves in accordance with the object to be detected, such as the drive shaft of a motor, and an optical unit 10 positioned opposite the reflective member 70, which irradiates light toward the reflective member 70, receives the light reflected by the reflective member 70, and generates an electrical signal corresponding to the intensity of the received light. The reflective member 70 is a thin, disc-shaped member with a plurality of slits 71 arranged along its circumference. Of course, the reflective member 70 can be any type of reflective member used in general encoders, such as one in which an optical pattern is formed with a reflective part that reflects light and a non-reflective part that does not reflect light. The optical unit 10 has a substrate 20. On the surface of the substrate 20 (i.e., on the same plane), a light-emitting part 30 and a light-receiving part 40 having a U-shape that surrounds the light-emitting part 30 are arranged opposite each other via the reflective member 70.

[0010] The light-emitting unit 30 has a light source such as an infrared LED or a semiconductor laser. The light-emitting unit 30 is positioned on the substrate 20 such that its light-emitting surface is parallel to the surface of the substrate 20, and is electrically connected to the electrodes (terminals) 23 of the substrate 20 at electrodes 33 provided on its back surface. The light generated by the light-emitting unit 30 is irradiated onto the reflective member 70 from the light-emitting surface.

[0011] The light-receiving unit 40 has a photoelectric conversion element such as a photodiode and generates an electrical signal corresponding to the intensity of the received light. The light-receiving unit 40 is positioned on the substrate 20 such that its light-receiving surface is parallel to the surface of the substrate 20, and is electrically connected to the electrode (terminal) 21 of the substrate 20 by a bonding wire 50 at a terminal 41 provided on its surface. The bonding wire 50 is a thin metal wire and has a loop shape that protrudes from the light-receiving unit 40 towards the reflective member 70 from the terminal 21 on the substrate 20. The light-emitting unit 30, the light-receiving unit 40, and the bonding wire 50 are covered by a light-transmitting protective member 60. The bonding wire 50 is an example of a connecting wire and may be a thin cable or the like.

[0012] The heights of the light-emitting section 30, the light-receiving section 40, and the bonding wire 50 from the surface of the substrate 20 have the following relationship. As shown in Figure 2, the height H02 from the surface of the substrate 20 to the surface (light-receiving surface) of the light-receiving section 40 is lower than the height H03 from the surface of the substrate 20 to the highest point of the bonding wire 50. Also, the height H02 from the surface of the substrate 20 to the surface (light-receiving surface) of the light-receiving section 40 is the same as the height H01 from the surface of the substrate 20 to the surface (light-emitting surface) of the light-emitting section 30. By making the height H02 from the surface of the substrate 20 to the surface of the light-receiving section 40 and the height H01 from the surface of the substrate 20 to the surface of the light-emitting section 30 the same, the optical design can be simplified and the unnecessary enlargement of the optical unit 10 can be suppressed.

[0013] The protective member 60 is made of a highly transparent resin such as epoxy resin, silicone resin, or acrylic resin. By covering the light-emitting part 30, the light-receiving part 40, and the bonding wire 50 with the protective member 60, environmental resistance and mechanical strength are improved, which can lead to improved reliability and a longer lifespan for the encoder.

[0014] The protective member 60 does not have a uniform height throughout, but has at least two different heights. This is one of the features of the encoder 1 according to this embodiment. Here, height refers to the distance from the surface of the substrate 20 to the surface of the protective member 60. As shown in Figure 2, in this embodiment, the protective member 60 has two different heights: a first height H11 (= H12) corresponding to the portion covering the light-emitting portion 30 and the light-receiving portion 40, and a second height H13 corresponding to the portion covering the bonding wire 50. The first height H11 is lower than the second height H13. Typically, the first height H11 is at least 1 / 4 and no more than 3 / 4 of the second height H13, and preferably 1 / 2 of the height.

[0015] As a method for forming the protective member 60, for example, a method using a mold can be employed. In this method, two molds having different heights are prepared, the assembled substrate 20 is set upside down in the mold, resin is poured in, and the protective member 60 can be formed by curing. The assembled substrate 20 refers to a substrate 20 on which the light-emitting part 30 and the light-receiving part 40 are mounted, and the terminals 41 of the light-receiving part 40 and the terminals 21 of the substrate 20 are connected by bonding wires 50. Alternatively, as in the conventional method, a protective member with a uniform height covering the bonding wires 50 may be formed, and then the protective member covering the light-emitting part 30 and the light-receiving part 40 may be shaved off with a drill or the like to reduce its height from the substrate 20.

[0016] The following explanation, with reference to Figures 2, 3, 4, and 5, describes the change in the angle of light incident on the light-receiving surface caused by making the first height H11 (= H12), which corresponds to the portion covering the light-emitting portion 30 and the light-receiving portion 40, lower than the second height H13, which corresponds to the portion covering the bonding wire 50.

[0017] Figures 2 and 3 show diagrams relating to the encoder according to this embodiment, and Figures 4 and 5 show diagrams relating to a conventional encoder. Figure 3 corresponds to Figure 2 and shows an example of the optical path of light generated by the light-emitting unit 30 and received by the light-receiving unit 40. Figure 4 is a cross-sectional view showing a conventional encoder corresponding to Figure 2. The conventional encoder 9 shown in Figure 4 is the same as the encoder 1 according to this embodiment shown in Figure 2, except for the protective member 61, and the protective member 61 has a uniform height H13 that can cover the bonding wire 50. Figure 5 corresponds to Figure 4 and shows an example of the optical path of light generated by the light-emitting unit 30 and received by the light-receiving unit 40. In Figures 3 and 5, the optical path of light emitted from a specific light-emitting point on the light-emitting surface and incident on a specific light-receiving point on the light-receiving surface is shown. In Figures 3 and 5, the refractive index of the protective members 60 and 61 is denoted as N1, the refractive index of air as N2, the horizontal distance from the light-emitting point to the light-receiving point as L, and the height (vertical distance) from the light-receiving surface of the light-receiving part 40 to the reflective member 70 as T0. These values ​​are common to both Figure 3 and Figure 5.

[0018] In Figure 3, the angle of emission of light from the light-emitting point to the reflecting member 70 is denoted as θ1, the angle of refraction between the protective member 60 and the air layer is denoted as θr1, and the angle of incidence of light from the reflecting member 70 through the protective member 60 to the light-receiving point is denoted as θ1. The angle of emission of light from the light-emitting point to the reflecting member 70 and the angle of incidence of light from the reflecting member 70 through the protective member 60 to the light-receiving point are the same and are therefore denoted the same. In this case, according to Snell's law, equation (1) holds between the angle of incidence (emission angle) θ1 and the angle of refraction θr1. Note that the angle of emission, angle of incidence, and angle of refraction represent the inclination with respect to the vertical axis.

[0019]

[0020] In Figure 3, the thickness of the protective member 60 covering the light-emitting section 30 and the light-receiving section 40 is denoted as T1. The thickness of the protective member 60 covering the light-emitting section 30 represents the distance from the light-emitting surface of the light-emitting section 30 to the surface of the protective member 60, and the thickness of the protective member 60 covering the light-receiving section 40 represents the distance from the light-receiving surface of the light-receiving section 40 to the surface of the protective member 60. In this case, the horizontal distance L can be expressed by equation (2). Typically, the thickness T1 has a height of 1 / 4 or more and 3 / 4 or less of the height T0 from the light-receiving surface of the light-receiving section 40 to the reflective member 70, and preferably has a height of 1 / 2.

[0021]

[0022] Similarly, in Figure 5, the angle of emission of light from the light-emitting point to the reflecting member 70 is denoted as θ2, the angle of refraction between the protective member 61 and the air layer is denoted as θr2, and the angle of incidence of light passing from the reflecting member 70 through the protective member 61 to the light-receiving point is denoted as θ2. The angle of emission of light from the light-emitting point to the reflecting member 70 and the angle of incidence of light passing from the reflecting member 70 through the protective member 61 to the light-receiving point are the same, so they are denoted the same way. In this case, according to Snell's law, equation (3) holds between the angle of incidence (emission angle) θ2 and the angle of refraction θr2.

[0023]

[0024] In Figure 5, the thickness of the protective member 61 covering the light-emitting section 30 and the light-receiving section 40 is denoted as T2. In this case, the horizontal distance L can be expressed by equation (4). Typically, the thickness T2 has a height of 5 / 8 or more and 7 / 8 or less of the height T0 from the light-receiving surface of the light-receiving section 40 to the reflective member 70, and preferably has a height of 3 / 4.

[0025]

[0026] Equation (5), which expresses the relationship between θ1 and θ2, can be derived from equations (1) to (4).

[0027]

[0028] From equation (5), the relative thicknesses T1 and T2 of the protective members 60 and 61 (T1 < T2), the angular range of the incident angle θ1 (0° < θ1 < 90°), and the angular range of the incident angle θ2 (0° < θ2 < 90°), the relative magnitude of θ1 and θ2 (θ1 < θ2) can be derived. The fact that θ1 is smaller than θ2 means that in the encoder 1 according to this embodiment, the light incident on the light-receiving surface of the light-receiving unit 40 is closer to perpendicular to the light-receiving surface than the light incident on the light-receiving surface of the light-receiving unit 40 in the conventional encoder 9.

[0029] According to this embodiment, compared to the conventional, the angle of light incident on the light-receiving surface can be brought closer to an angle perpendicular to the light-receiving surface. This makes it possible to improve the energy density of light per unit area on the light-receiving surface. In addition, the optical path length passing through the protective member 60 can be shortened, and the loss of light energy associated with passing through the protective member 60 can be suppressed. Furthermore, since the protective member 60 itself is thinner than in the conventional, the optical path length passing through the protective member 60 can naturally be shortened, and the loss of light energy associated with passing through the protective member 60 can be suppressed. As a result, the encoder 1 according to this embodiment can improve the light-receiving sensitivity of the light-receiving unit 40 compared to the conventional encoder 9.

[0030] The encoder may have multiple light-receiving units. Figure 6 is a cross-sectional view showing the configuration of an encoder according to a first modified example of this embodiment. As shown in Figure 6, the encoder 2 according to the first modified example has two light-receiving units: a first light-receiving unit 40 and a second light-receiving unit 45. The first light-receiving unit 40 is electrically connected to an electrode (terminal) 21 of the substrate 20 by a first bonding wire 50 at a terminal 41 provided on its surface. The second light-receiving unit 45 is electrically connected to an electrode (terminal) 26 of the substrate 20 by a second bonding wire 55 at a terminal 46 provided on its surface. The protective member 62 has two types of heights: a first height H11 (= H12 = H14) corresponding to the portion that covers the light-emitting unit 30, the first light-receiving unit 40, and the second light-receiving unit 45, and a second height H13 (= H15) corresponding to the portion that covers the first bonding wire 50 and the second bonding wire 55. The first height H11 is lower than the second height H13. The encoder 2 according to the first modified example configured in this way provides the same effects as the encoder 1 according to the present embodiment. Of course, if the height H11 corresponding to the portion covering the light-emitting portion 30, the height H12 corresponding to the portion covering the first light-receiving portion 40, and the height H14 corresponding to the portion covering the first light-receiving portion 45 are lower than the height H13 of the portion covering the first bonding wire 50 and the height H15 of the portion covering the second bonding wire 55, then the height H11 corresponding to the portion covering the light-emitting portion 30, the height H12 corresponding to the portion covering the first light-receiving portion 40, and the height H14 corresponding to the portion covering the second light-receiving portion 45 may be different heights from each other, and the height H13 of the portion covering the first bonding wire 50 and the height H15 of the portion covering the second bonding wire 55 may be different heights from each other.

[0031] The light-emitting part may be electrically connected to the substrate by bonding wires. Figure 7 is a cross-sectional view showing the configuration of an encoder according to a second modified example of this embodiment. As shown in Figure 7, in the encoder 3 according to the second modified example, the light-emitting part 35 is electrically connected to the electrodes (terminals) 27 of the substrate 20 by bonding wires 57 at terminals 37 provided on its surface. The protective member 63 has two heights: a first height H11 (= H12) corresponding to the portion that covers the light-emitting part 35 and the light-receiving part 40, and a second height H13 (= H16) corresponding to the portion that covers the bonding wires 57 that electrically connect the light-emitting part 35 and the substrate 20, and the bonding wires 50 that electrically connect the light-receiving part 40 and the substrate 20. The first height H11 is lower than the second height H13. The encoder 3 according to the second modified example configured in this way provides the same effects as the encoder 1 according to this embodiment. Of course, if the height H11 corresponding to the portion covering the light-emitting portion 35 and the height H12 corresponding to the portion covering the light-receiving portion 40 are lower than the height H16 corresponding to the portion covering the bonding wire 57 that electrically connects the light-emitting portion 35 and the substrate 20 and the height H13 corresponding to the portion covering the bonding wire 50 that electrically connects the light-receiving portion 40 and the substrate 20, then the height H11 corresponding to the portion covering the light-emitting portion 35 and the height H12 corresponding to the portion covering the light-receiving portion 40 may be different heights, and the height H16 corresponding to the portion covering the bonding wire 57 that electrically connects the light-emitting portion 35 and the substrate 20 and the height H13 corresponding to the portion covering the bonding wire 50 that electrically connects the light-receiving portion 40 and the substrate 20 may be different heights.

[0032] The encoder 1 according to this embodiment can also be applied to a linear encoder that detects the distance traveled, speed, and direction of movement of an object to be detected. In that case, the reflective member 70 is made of a thin rectangular plate material with a plurality of slits 71 arranged along one direction. Even with a linear encoder, the same effects as in this embodiment can be achieved.

[0033] The substrate 20 described in this embodiment is an example of a plate-shaped member. The plate-shaped member is not limited to the substrate 20, as long as it can fix the light-emitting part 30 and the light-receiving part 40 and has multiple terminals to which the light-emitting part 30 and the light-receiving part 40 can be electrically connected. For example, the plate-shaped member may be a plate material that does not have a conductive pattern with multiple holes. Furthermore, the substrate 20 in this embodiment refers to general types such as a single-sided substrate with a conductive pattern formed on only one side, a double-sided substrate with conductive patterns formed on both sides, a multilayer substrate having a conductive layer inside, and a flexible substrate that is flexible.

[0034] The light-emitting unit 30 and the light-receiving unit 40 can be freely mounted on the substrate 20 from various perspectives, provided that the height H01 from the surface of the substrate 20 to the surface of the light-emitting unit 30 and the height H02 from the surface of the substrate 20 to the surface of the light-receiving unit 40 are both lower than the height H03 from the surface of the substrate 20 to the highest point of the bonding wire 50. For example, to avoid a situation where light generated by the light-emitting unit 30 is received directly by the light-receiving unit 40 without passing through the reflective member 70, the light-emitting unit 30 may be mounted at a higher position than the light-receiving unit 40. That is, the light-emitting unit 30 and the light-receiving unit 40 may be mounted on the substrate 20 such that the height H01 from the surface of the substrate 20 to the surface of the light-emitting unit 30 is higher than the height H02 from the surface of the substrate 20 to the surface of the light-receiving unit 40. Also, to enable the light-receiving unit 40 to receive light reflected by the reflective member 70 with high efficiency, the light-receiving unit 40 may be mounted at a higher position than the light-emitting unit 30 (closer to the reflective member 70). In other words, the light-emitting unit 30 and the light-receiving unit 40 may be mounted on the substrate 20 such that the height H02 from the surface of the substrate 20 to the surface of the light-receiving unit 40 is higher than the height H01 from the surface of the substrate 20 to the surface of the light-emitting unit 30.

[0035] The following further notes are disclosed regarding this embodiment and its modifications. (Note 1) The optical encoder 1 comprises a reflective member 70 having a plurality of arranged slits 71 that move in accordance with the object to be measured, a plate-shaped member 20, a light-emitting part 30 disposed on the plate-shaped member 20, a light-receiving part 40 disposed on the plate-shaped member 20 to face the light-emitting part 30 via the reflective member 70, a bonding wire 50 that electrically connects the light-receiving part 40 to a terminal on the plate-shaped member 20 and has a loop shape that protrudes from the light-receiving part 40 towards the reflective member 70, and a light-transmitting protective member 60 that covers the light-emitting part 30 and the light-receiving part 40, wherein the protective member 60 has a height lower than the height from the plate-shaped member 20 to the highest point of the bonding wire 50. (Note 2) In the optical encoder 1 described in Note 1, the protective member 60 covers the bonding wire 50 together with the light-emitting part 30 and the light-receiving part 40, and the height from the plate-shaped member 20 to the surface of the protective member 60 in the portion covering the light-emitting part 30 and the light-receiving part 40 is lower than the height from the plate-shaped member 20 to the surface of the protective member 60 in the portion covering the bonding wire 50. (Note 3) In the optical encoder 1 described in Note 1, the height from the plate-shaped member to the surface of the protective member in the portion covering the light-emitting part is the same as the height from the plate-shaped member to the surface of the protective member in the portion covering the light-receiving part. (Note 4) In the optical encoder 1 described in Note 1, an electrode 33 is provided on the back surface of the light-emitting part 30 facing the surface of the plate-shaped member 20, and the light-emitting part 30 is electrically connected to the plate-shaped member 20 at the electrode 33.

[0036] While embodiments of this disclosure have been described in detail, this disclosure is not limited to the individual embodiments described above. These embodiments can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the spirit of the invention or the idea and spirit of the invention derived from the claims and their equivalents. For example, the order of operations and processes in the embodiments described above are shown as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments described above.

[0037] 1...Optical encoder, 10...Optical unit, 20...Substrate, 30...Light-emitting part, 40...Light-receiving part, 50...Bonding wire, 60...Protective member.

Claims

1. An optical encoder comprising: a reflective member having a plurality of arranged slits that move in accordance with an object to be measured; a plate-shaped member; a light-emitting part disposed on the plate-shaped member; a light-receiving part disposed on the plate-shaped member to face the light-emitting part via the reflective member; a bonding wire having a loop shape that electrically connects the light-receiving part to a terminal on the plate-shaped member and protrudes toward the reflective member from the light-receiving part to the terminal; and a light-transmitting protective member that covers the light-emitting part and the light-receiving part, wherein the protective member has a height lower than the height from the plate-shaped member to the highest point of the bonding wire.

2. The optical encoder according to claim 1, wherein the protective member covers the bonding wire together with the light-emitting portion and the light-receiving portion, and the height from the plate-shaped member to the surface of the protective member in the portion covering the light-emitting portion and the light-receiving portion is lower than the height from the plate-shaped member to the surface of the protective member in the portion covering the bonding wire.

3. The optical encoder according to claim 1, wherein the height from the plate-shaped member to the surface of the protective member in the portion covering the light-emitting portion is the same as the height from the plate-shaped member to the surface of the protective member in the portion covering the light-receiving portion.

4. An electrode is provided on the back surface of the light-emitting portion facing the surface of the plate-shaped member, and the light-emitting portion is electrically connected to the plate-shaped member at the electrode, as described in claim 1.

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