Reflective Optical Sensor

Abstract

[Problem] To provide a reflection-type optical sensor that can improve coupling efficiency. [Solution] A reflection-type optical sensor (1), in which a light reception element (4) senses reflected light in which light from a light emission element (3) is reflected by an object (OB) being sensed, has an open-box-shaped case (2) provided at a bottom section with first and second concave mirrors (5, 6). The first and second concave mirrors (5, 6) are formed so that parabolic surfaces that include the vertices of parabolas obtained by rotating a parabola around the axis of symmetry of the concave mirrors are reflective surfaces, the reflective surfaces being oriented to the open side of the case (2) so that an axis of symmetry (A1) passing through a first focal point (F1) of the first concave mirror (5) and an axis of symmetry (A2) passing through a second focal point (F2) of the second concave mirror (6) intersect at a prescribed intersection angle on the side opposite from the vertex (V1) of the first concave mirror (5) with respect to the first focal point (F1) and on the side opposite from the vertex (V2) of the second concave mirror (6) with respect to the second focal point (F2). The light emission element (3) emits light toward the first concave mirror (5) from the first focal point (F1) or the vicinity of the first focal point (F1). Of the light reflected by the first concave mirror (5), the reflected light reflected by the object (OB) being sensed is reflected by the second concave mirror (6) so as to be focused toward the second focal point (F2), and is sensed by the light reception element (4).

Description

[Technical field]

[0001] The present invention relates to a reflective optical sensor that detects an object by irradiating light and detecting the light reflected by the object. [Background technology]

[0002] Reflective optical sensors have been widely used in the past to detect objects by irradiating light and detecting the light reflected by a nearby object. Reflective optical sensors are capable of detecting objects without contact, and are therefore commonly used in applications such as detecting rotation angles and object edges.

[0003] A reflective optical sensor, as in Patent Document 1, for example, has a light-emitting element, a light-receiving element, and a light-shielding wall disposed between them, and is configured so that light emitted by the light-emitting element is reflected by the object to be detected and this reflected light is received by the light-receiving element. The output of the light-receiving element fluctuates depending on the presence or absence of reflected light and the intensity of the reflected light, and this is utilized to detect the object to be detected. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-308372 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the reflective optical sensor of Patent Document 1, the light-emitting element irradiates diffused light onto a nearby object to be detected. Therefore, most of the light emitted by the light-emitting element is irradiated onto the object to be detected, but even if the object to be detected has a high reflectance, only a small amount of the light reflected by the object is incident on the light-receiving element. For example, when the ratio of the light emitted by the light-emitting element to the light that is incident on the light-receiving element is defined as the coupling efficiency, the results of a ray tracing simulation of the reflective optical sensor of Patent Document 1 show that the coupling efficiency is about 5% when the illumination angle of the light-emitting element is 90°, and there is a demand for an improvement in the coupling efficiency.

[0006] An object of the present invention is to provide a reflective optical sensor capable of improving coupling efficiency. [Means for solving the problem]

[0007] The reflective optical sensor of the invention of claim 1 includes a light-emitting element and a light-receiving element, and detects an object by the light-receiving element detecting light reflected from the light-emitting element by the object, the reflective optical sensor having an open box-like case with a first concave mirror and a second concave mirror integrally formed at a bottom thereof, the first concave mirror and the second concave mirror each have a reflective surface which is a paraboloid including an apex of a parabola formed by rotating the parabola around an axis of symmetry of the parabola, and the reflective surface is formed facing the open side of the case such that the axis of symmetry of the first concave mirror and the axis of symmetry of the second concave mirror intersect at a predetermined intersection angle on the opposite side of the apex of the first concave mirror with respect to a first focal point of the first concave mirror and on the opposite side of the apex of the second concave mirror with respect to a second focal point of the second concave mirror, a pair of first lead frames and a pair of second lead frames are fixed to an open-side end of the case, the pair of first lead frames extending opposite each other along a plane including the open-side end face of the case and with their tips close to each other; the light-emitting element is fixed to the first concave mirror side of one tip of the first lead frame so that its light-emitting surface faces the first concave mirror and is located at or near the first focal point, and is housed in the case; the light-receiving element is fixed to the second concave mirror side of one tip of the second lead frame so that its light-receiving surface faces the second concave mirror and is located at or near the second focal point, and is housed in the case; the case is filled with a sealing resin through which light from the light-emitting element passes, covering the light-emitting element and the light-receiving element, and a surface of the sealing resin is formed that is parallel to a plane including the first focal point and the second focal point and coincides with the open-side end face; The light emitting element is configured so that the light is irradiated toward the first concave mirror, which reflects the light and irradiates it onto the object to be detected, the reflected light reflected by the object to be detected is irradiated onto the second concave mirror, and the reflected light reflected by the second concave mirror so as to be focused toward the second focal point is detected by the light receiving element.

[0008] According to the above configuration, the light emitting element of the reflective optical sensor irradiates light from the position of the first focal point of the first concave mirror or a position near the first focal point toward the first concave mirror, and the light reflected by the first concave mirror is irradiated onto the object to be detected. The reflected light reflected by the object to be detected is irradiated onto the second concave mirror, and the reflected light reflected by the second concave mirror so as to be focused toward the second focal point is incident on the light receiving element of the reflective optical sensor. The light emitted from the light emitting element is reflected by the first concave mirror to become parallel light due to the nature of the parabolic surface, so that a constant amount of light is irradiated onto the object to be detected regardless of the distance to the object. When the irradiated parallel light is reflected by the flat reflecting surface of the object to be detected, most of the reflected light is irradiated onto the second concave mirror as parallel light, and is reflected and focused by the second concave mirror toward the second focal point. Therefore, most of the diffuse light irradiated from the light-emitting element is converted into parallel light and irradiated onto the object to be detected, and the reflected light is collected and detected by the light-receiving element, so that the coupling efficiency can be improved when the ratio of the light emitted by the light-emitting element to the light that is incident on the light-receiving element is taken as the coupling efficiency. In addition, since parallel light is irradiated, a constant light can be irradiated regardless of the distance from the reflective optical sensor, and the range of distances between the object to be detected and the reflective optical sensor at which high coupling efficiency can be obtained can be widened.

[0009] In addition, the light emitting element and the light receiving element housed in the case are covered with the sealing resin by filling the case with a sealing resin that transmits light from the light emitting element up to the open end face of the case, The light emitting element, the light receiving element and the reflecting surfaces of the first and second concave mirrors are protected, and damage to the reflective optical sensor due to collision with an object to be detected can be prevented.

[0010] Claim 2 The reflective optical sensor of the present invention, in the invention of claim 1, is characterized in that it has a light-shielding wall between the first concave mirror and the second concave mirror, which prevents light from the light-emitting element from directly entering the second concave mirror and prevents light reflected by the first concave mirror from directly entering the light-receiving element. According to the above configuration, light from the light-emitting element is prevented from being reflected by the object to be detected and entering the light-receiving element, thereby making it possible to prevent erroneous detection of the object to be detected. Effect of the Invention

[0011] According to the reflective optical sensor of the present invention, the coupling efficiency can be improved. [Brief description of the drawings]

[0012] [Figure 1] 1 is a plan view of a reflective optical sensor according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. [Figure 4] FIG. 2 is an explanatory diagram for assembling a reflective optical sensor. [Diagram 5] 13 is an example of a ray tracing simulation result for a reflective optical sensor according to an embodiment. [Figure 6] FIG. 11 is a diagram showing the relationship between the distance h and the coupling efficiency in the reflective optical sensor according to the embodiment. [Figure 7] 11 is a diagram showing, in the form of contour lines, the relationship between the distance h, the angles of the first and second concave mirrors, and the coupling efficiency in the reflective optical sensor in the example. FIG. [Figure 8] 6 is a diagram showing the relationship between the angles of the first and second concave mirrors, the focal lengths of the first and second concave mirrors, and the coupling efficiency in the reflective optical sensor of the embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the mode for carrying out the present invention will be described based on examples. EXAMPLES

[0014] 1 and 2, the reflective optical sensor 1 has an open box-shaped case 2 with an open top surface, a light-emitting element 3, and a light-receiving element 4. Note that the open side of the case 2 will be described as the upper side of the reflective optical sensor 1, but the reflective optical sensor 1 can be used in various positions depending on the application, etc.

[0015] A first concave mirror 5 and a second concave mirror 6 are integrally formed on the bottom inside the case 2 with their reflective surfaces facing the open side of the case 2. The first concave mirror 5 is a paraboloid formed by rotating the parabola P1 around its axis of symmetry A1, and is formed with a paraboloid including the apex of the parabola P1 as its reflective surface. The second concave mirror 6 is a paraboloid formed by rotating the parabola P2 around its axis of symmetry A2, and is formed with a paraboloid including the apex of the parabola P2 as its reflective surface.

[0016] As shown in Figure 3, y=x on the xy plane. 2 For example, in the parabola P expressed by / (4a), = 5 mm for parabolas P1 and P2, but the value of a may be different for parabola P1 and parabola P2. Note that the y-axis is the axis of symmetry of parabola P, the position of the origin is the vertex of parabola P, and the position (x, y) = (0, a) is the focus of parabola P.

[0017] As shown in Figs. 1 and 2, the apex of the parabola P1 forming the first concave mirror 5 is the first apex V1, and the focus is the first focus F1. The apex of the parabola P2 forming the second concave mirror 6 is the second apex V2, and the focus is the second focus F2. The first concave mirror 5 and the second concave mirror 6 are formed so that the symmetry axis A1 passing through the first apex V1 and the first focus F1 of the parabola P1 and the symmetry axis A2 passing through the second apex V2 and the second focus F2 of the parabola P2 intersect at a predetermined intersection angle 2θ. In this case, it is preferable that the symmetry axes A1 and A2 are inclined symmetrically at an angle θ with respect to a direction axis perpendicular to the open-side end face 2e of the case 2 (the normal N of the open-side end face 2e passing through the intersection of the symmetry axes A1 and A2).

[0018] The symmetry axes A1 and A2 intersect on the opposite side of the first vertex V1 with respect to the first focal point F1 and on the opposite side of the second vertex V2 with respect to the second focal point F2. That is, the symmetry axes A1 and A2 intersect at a position farther away than the first focal point F1 and the second focal point F2 on the opposite side of the first and second vertices V1 and V2.

[0019] The case 2 is formed, for example, by resin molding, into a rectangular parallelepiped box shape with an open top surface, and paraboloids are formed on the inside bottom by rotating parabolas P1, P2 corresponding to the first and second concave mirrors 5, 6. Reflective films 5a, 6a containing a metal such as gold or titanium are formed on at least these two paraboloids, respectively, and the first and second concave mirrors 5, 6 are formed integrally with the case 2. At the boundary between the first concave mirror 5 and the second concave mirror 6, a light-shielding wall 7 is formed extending from the inside bottom of the case 2 toward the open side so as to separate the first concave mirror 5 and the second concave mirror 6.

[0020] At the open end of the case 2, recesses 2a to 2d are formed by recessing from the open end face 2e of the case 2 toward the bottom side in order to position a pair of first lead frames 8a, 8b and a pair of second lead frames 9a, 9b. The first lead frames 8a, 8b supply power to the light emitting element 3 from the outside. The light emitting element 3 is fixed to one side of the tip of the first lead frame 8a, which is placed and fixed in the recess 2a. The first lead frame 8a is fixed to the recess 2a so that the light emitting surface from which the light of the light emitting element 3 is emitted faces the first concave mirror 5 and the light emitting element 3 is positioned at the position of the first focal point F1 or in a position near there. At this time, the light emitting element 3 is accommodated in the case 2. It is to be noted that the recesses 2a to 2d may not be formed and the position may be determined by another method.

[0021] The second lead frames 9a, 9b output the optical power of the light receiving element 4 to the outside. The light receiving element 4 is fixed to one side of the tip of the second lead frame 9a, which is placed and fixed in the recess 2c. The second lead frame 9a is fixed to the recess 2c so that the light receiving surface of the light receiving element 4, which receives incident light, faces the second concave mirror 6 and so that the light receiving element 4 is located at the position of the second focal point F2 or a position nearby it. At this time, the light receiving element 4 is accommodated in the case 2.

[0022] As shown in FIG. 2, the case 2 housing the light-emitting element 3 and the light-receiving element 4 is filled with a sealing resin 10, and the light-emitting element 3 and the light-receiving element 4 are covered with the sealing resin 10. The first lead frames 8a, 8b and the second lead frames 9a, 9b may also be covered with the sealing resin 10. The sealing resin 10 is a translucent resin that transmits the light of the light-emitting element 3, for example, an epoxy-based synthetic resin that transmits visible light or infrared light. The sealing resin 10 protects the reflecting surfaces of the light-emitting element 3, the light-receiving element 4, and the first and second concave mirrors 5, 6, and regulates the oscillation of the light-emitting element 3 and the light-receiving element 4. For example, when vibrations are not transmitted from the outside to the light-emitting element 3 and the light-receiving element 4, the sealing resin 10 may be omitted.

[0023] The surface 10a of the sealing resin 10 is formed flat so as to coincide with the open end surface 2e of the case 2. The surface 10a of the sealing resin 10 is a plane in the vicinity of the first focal point F1 and the second focal point F2, which is parallel to a plane including the first focal point F1 and the second focal point F2. The intersection of the symmetry axis A1 and the symmetry axis A2 above the surface 10a of the sealing resin 10 and the area in the vicinity of this intersection are the detection position of the object to be detected.

[0024] Since the first lead frames 8a, 8b and the second lead frames 9a, 9b are elongated members made of, for example, kovar (an alloy containing iron, nickel, and cobalt), it is not easy to attach them to the case 2 individually. Therefore, as shown in FIG. 4, the light emitting element 3 and the light receiving element 4 are fixed to the first lead frames 8a, 8b and the second lead frames 9a, 9b formed integrally with a rectangular frame 11, and are electrically connected by, for example, bonding wires. Then, the first lead frames 8a, 8b and the second lead frames 9a, 9b are simultaneously placed together with the frame 11 in the corresponding recesses 2a to 2d. After sealing with the sealing resin 10, the base ends of the first lead frames 8a, 8b and the second lead frames 9a, 9b are cut to separate and remove the frame 11.

[0025] The frame 11 having the first lead frames 8a, 8b and the second lead frames 9a, 9b can be formed in a tape or sheet shape so that the frame 11 is connected in a plane. In this case, the light emitting element 3 and the light receiving element 4 can be easily fixed and electrically connected, and they can be attached consecutively or simultaneously to a plurality of cases 2 arranged at predetermined intervals, for example, improving manufacturing efficiency.

[0026] 5, due to the nature of a parabola, a part of the light i1 irradiated from the light-emitting element 3 at or near the first focal point F1 can be reflected by the first concave mirror 5 and irradiated to the object to be detected OB as light i2 (parallel light). The light-shielding wall 7 prevents the light irradiated from the light-emitting element 3 from directly entering the second concave mirror 6, and also prevents the light reflected by the first concave mirror 5 from directly entering the light-receiving element 4. The light-emitting element 3 is a light-emitting diode with an irradiation angle of 90°.

[0027] When an object to be detected OB having a flat reflecting surface parallel to the surface 10a of the sealing resin 10 of the reflective optical sensor 1 is present at the detection position, the light i2 is reflected by the object to be detected OB, and the reflected light i3 (parallel light) is irradiated onto the second concave mirror 6. At this time, when the symmetry axes A1 and A2 are inclined symmetrically at the same angle with respect to the surface 10a, it is easy to set the reflective surface of the object to be detected OB and the surface 10a of the reflective optical sensor 1 so that they are parallel. Even if the symmetry axes A1 and A2 are not inclined symmetrically at the same angle with respect to the surface 10a, the object to be detected OB can be detected by setting the reflective surface of the object to be detected OB so that it is inclined with respect to the surface 10a.

[0028] The reflected light i3 is reflected by the second concave mirror 6 toward the second focal point F2 and is collected as reflected light i4. The reflected light i4 is then incident on the light receiving element 4 at or near the position of the second focal point F2, and a photocurrent is output. On the other hand, when there is no object to be detected OB, a part of the light from the light-emitting element 3 is reflected by the first concave mirror 5, and the light i2 goes outside and does not enter the second concave mirror 6, and therefore does not enter the light receiving element 4. Therefore, the reflective optical sensor 1 can detect the object to be detected OB by reflecting the reflected light i3, which is the light from the light-emitting element 3 reflected by the object to be detected OB, by the second concave mirror 6 and detecting this reflected light i4 by the light receiving element 4.

[0029] When the ratio of light incident on the light receiving element 4 to the light irradiated by the light emitting element 3 is taken as the coupling efficiency, the higher the coupling efficiency, the larger the photocurrent output of the reflective optical sensor 1. Therefore, it is desirable to achieve a high coupling efficiency, since it is possible to easily prevent erroneous detection of the object OB due to the influence of stray light, for example, and it is also possible to reduce power consumption by reducing the amount of light from the light emitting element 3, for example. Here, based on the ray tracing simulation shown in FIG. 5, the coupling efficiency when the object OB is separated from the surface 10a of the reflective optical sensor 1 is shown in FIG. 6, with the distance h between the surface 10a and the object OB as a parameter.

[0030] As the distance h is increased, the coupling efficiency increases up to h=3.7 mm, after which the coupling efficiency becomes constant at 52%. As the distance h is further increased, the coupling efficiency decreases. The coupling efficiency is maximum when the distance h is in the range of 3.7 mm to 5.7 mm, and a high coupling efficiency exceeding 10% is obtained when the distance h is approximately 0 mm to 8 mm. Therefore, even if a certain distance h is secured to prevent damage to the reflective optical sensor 1 and the detected object OB due to contact between the reflective optical sensor 1 and the detected object OB, a high coupling efficiency can be secured. Also, when the detected object OB is smaller than the irradiation range of the irradiated parallel light, the reflected light decreases, but the high coupling efficiency allows the small detected object OB to be detected.

[0031] The coupling efficiency when the distance h and the inclination angle θ of the symmetric axes A1, A2 (the inclination angle of the first and second concave mirrors 5, 6) are used as parameters is shown in the form of contour lines in FIG. 7. As the angle θ increases, the range of the distance h where high coupling efficiency is obtained shifts in the direction in which the distance h decreases. When the angle θ is increased to a certain extent, most of the light reflected by the first concave mirror 5 is blocked by the light-shielding wall 7 so as not to be directly incident on the light receiving element 4, and is no longer irradiated to the object to be detected OB, so that the coupling efficiency drops sharply. When the distance h is set, the reflective optical sensor 1 can be formed at the angle θ at which the coupling efficiency is high based on FIG. 7. For the reflective optical sensor 1 with the angle θ, the optimal distance h at which the coupling efficiency is high can be specified.

[0032] When the distance h is 5 mm, the coupling efficiency when the tilt angle θ and focal length of the first and second concave mirrors 5, 6 are used as parameters is shown by a curved surface in Figure 8. The coupling efficiency is hardly affected by the focal lengths of the first and second concave mirrors 5, 6, and is maximum when the angle θ is 25° at any focal length.

[0033] The function and effect of the reflective optical sensor 1 will now be described. In the reflective optical sensor 1, the light emitting element 3 irradiates light i1 toward the first concave mirror 5 from the position of the first focal point F1 of the first concave mirror 5 or a position in the vicinity of this first focal point F1, and the light i2 reflected by the first concave mirror 5 is irradiated onto the object to be detected OB. The reflected light i3 reflected by the object to be detected OB is irradiated onto the second concave mirror 6, and the reflected light i4 reflected by the second concave mirror 6 so as to be condensed toward the second focal point F2 is incident on the light receiving element 4.

[0034] The light i1 emitted from the light-emitting element 3 is reflected by the first concave mirror 5 and becomes parallel light due to the nature of the parabolic surface, so that a constant light i2 is irradiated regardless of the distance from the reflective optical sensor 1 and reflected by the object to be detected OB. Most of the reflected light i3 reflected by the flat reflecting surface of the object to be detected OB is irradiated to the second concave mirror 6 as parallel light, and is reflected and collected by the second concave mirror 6 toward the second focal point F2. Therefore, most of the diffuse light irradiated from the light-emitting element 3 is made parallel light and irradiated to the object to be detected OB, and the reflected light i3 is collected and detected by the light-receiving element 4, so that the coupling efficiency can be improved when the ratio of the light incident on the light-receiving element 4 to the light emitted by the light-emitting element 3 is defined as the coupling efficiency. In addition, since parallel light is irradiated, a constant light can be irradiated to the object to be detected OB regardless of the distance from the reflective optical sensor 1, and the range of the distance h between the object to be detected OB and the reflective optical sensor 1 where a high coupling efficiency is obtained can be widened.

[0035] The case 2 contains the light-emitting element 3 and the light-receiving element 4 and is filled with a sealing resin 10 that transmits light from the light-emitting element 3. Therefore, the sealing resin 10 protects the light-emitting element 3, the light-receiving element 4, and the reflective surfaces of the first and second concave mirrors 5 and 6, and can prevent damage to the reflective optical sensor 1 due to, for example, a collision with a detection object OB.

[0036] The reflective optical sensor 1 has a light-shielding wall 7 between the first concave mirror 5 and the second concave mirror 6, which prevents the light of the light-emitting element 3 from directly entering the second concave mirror 6 and prevents the light reflected by the first concave mirror 5 from directly entering the light-receiving element 4. This prevents the light of the light-emitting element 3 from being reflected by the object to be detected OB and entering the light-receiving element 4, thereby preventing erroneous detection of the object to be detected OB.

[0037] Although not shown in the figures, instead of the first lead frames 8a, 8b and the second lead frames 9a, 9b, the light emitting element 3 and the light receiving element 4 may be fixed to a lid member that is transparent to the light of the light emitting element 3, a plurality of wirings that are electrically connected to the light emitting element 3 and the light receiving element 4 may be formed on the lid member, and this lid member may be fixed to the open side of the case 2. In addition, a person skilled in the art may implement the present invention in a form in which various modifications are added to the above embodiment without departing from the spirit of the present invention, and the present invention also includes such modifications. [Explanation of symbols]

[0038] 1: Reflective optical sensor 2: Case 2a~2d: Concave part 2e: Open side end surface 3: Light emitting element 4: Light receiving element 5: 1st concave mirror 6:Second concave mirror 7: Shading wall 8a, 8b: first lead frame 9a, 9b: second lead frame 10: Sealing resin 10a: surface 11: Frame A1, A2: Axes of symmetry F1: 1st focal point F2: 2nd focal point P1, P2: Parabola V1, V2: vertices

Claims

1. A reflective optical sensor includes a light emitting element and a light receiving element, and detects an object by detecting light emitted from the light emitting element and reflected by the object using the light receiving element, a first concave mirror and a second concave mirror are integrally formed on a bottom of the open box-shaped case; the first concave mirror and the second concave mirror each have a reflective surface that is a paraboloid including an apex of a parabola formed by rotating the parabola around an axis of symmetry of the parabola, and are formed with the reflective surfaces facing the open side of the case such that the axis of symmetry of the first concave mirror and the axis of symmetry of the second concave mirror intersect at a predetermined intersection angle on the opposite side of the apex of the first concave mirror with respect to a first focal point of the first concave mirror and on the opposite side of the apex of the second concave mirror with respect to a second focal point of the second concave mirror, A pair of first lead frames and a pair of second lead frames are fixed to the open end of the case, the pair of first lead frames and second lead frames extending opposite to each other along a plane including the open end surface of the case and having their tips close to each other; the light emitting element is fixed to the first concave mirror side of one end portion of the first lead frame such that a light emitting surface faces the first concave mirror and is at or near the first focal point, and is accommodated in the case; the light receiving element is fixed to the second concave mirror side of one end portion of the second lead frame so that a light receiving surface faces the second concave mirror and is located at or near the second focal point, and is accommodated in the case; the case is filled with a sealing resin through which light from the light emitting element passes, covering the light emitting element and the light receiving element, and a surface of the sealing resin is formed that is parallel to a plane including the first focal point and the second focal point and coincides with the open end face; the light irradiated by the light emitting element toward the first concave mirror is reflected by the first concave mirror and irradiated onto the detection object; The light reflected by the object is irradiated onto the second concave mirror, a light receiving element that detects the reflected light reflected by the second concave mirror so as to be focused toward the second focal point;

2. 2. The reflective optical sensor according to claim 1, further comprising a light-shielding wall between the first concave mirror and the second concave mirror, the light-shielding wall preventing light from the light-emitting element from directly entering the second concave mirror and preventing light reflected by the first concave mirror from directly entering the light-receiving element.

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