Optical head unit of a photodetector

Abstract: A head unit of a photo detector for irradiating a target area with detection light having a pencil of rays substantially shaped like a belt in transverse section and receiving light reflected in the target area. The head unit includes a belt-like-light generation lens having different light gathering functions relative to two directions orthogonal to each other in the transverse section of the pencil of rays for generating detection light substantially shaped like a belt, a light emission section for emitting the detection light from a first interface of the belt-like-light generation lens through a second interface of the belt-like-light generation lens to the target area, and a light reception section for receiving reflected light incident on the light reception section through the first interface of the belt-like-light generation lens from the second interface.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a head unit of a photo detector. 2. Description of the Related Art Hitherto, a photo detector for irradiating a target area with detection light substantially shaped like a belt and receiving reflected light therefrom to detect a workpiece or the like has been known. FIG. 10(a) shows an example of the structure of a head unit of the photo detector. In FIG. 10(a), a head unit 100 comprises an alternating pattern of light emission optical fibers 102 and light reception optical fibers 103 arranged in and fixed to a case 101 with an end face exposed. However, in the related art, a large number of optical fibers 102 and 103 are arranged in the case 101, thus the head unit 100 is upsized. Since a large number of optical fibers are arranged in a row and fixed to the case 101, the manufacturability of the head unit 100 is poor. US 4,510,383, US 3,345,835 and EP-A-0 550 271 disclose a head unit according to the preamble of claim 1. SUMMARY OF THE INVENTION It is an object of the invention to miniaturize a head unit of a photo detector for irradiating a target area with detection light substantially shaped like a belt and receiving reflected light therefrom. At the same time, the detection accuracy of the head unit of the photo detector shall be improved. To accomplish the above object, according to the invention, there is provided a head unit of a photo detector for irradiating a target area with detection light having the features recited in claim 1. The spot-like light emitted from the light emission section is formed into detection light substantially shaped like a belt by the function of the optical system and the detection light is applied to the target area. The detection light is reflected by an object to be detected or the background in the target area and the reflected light is received at the light reception section through the optical system. According to a preferred embodiment of the invention, said light emission section is arranged for emitting the detection light from a first interface of the belt-like-light generation lens through a second interface of the belt-like-light generation lens to the target area; and said light reception section is arranged for receiving reflected light incident on the light reception section through the first interface of the belt-like-light generation lens from the second interface. The spot-like light emitted from the light emission section passes through the belt-like-light generation lens and is formed into detection light substantially shaped like a belt and the detection light is applied to the target area. The detection light is reflected by an object to be detected or the background in the target area and the reflected light passes through the belt-like-light generation lens and is received at the light reception section. In the invention, a lens is used as the "optical element for gathering light". More than one lens may be used. Generally, a bar-like lens such as a cylindrical lens or an elongated plate-like lens can be used. The "light gathering" or "gathering light" refers to making light attempted to spread at a predetermined divergence angle parallel light or making a divergence angle small in addition to converging light. Therefore, the light emitted from a point light source passes through the belt-like-light generation lens and becomes a pencil of rays substantially shaped like an elongated belt. In addition to the end faces of optical fibers, such elements as LED, LD, and PD can also be used as the "light emission section" and the "light reception section". BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: FIG. 1 is an exploded perspective view to show an embodiment of a head unit of the invention; FIG. 2 is an exploded perspective view to show an optical system; FIG. 3(a) is a sectional view to show the optical system, FIG. 3(b) is a characteristic chart to show change in light reception quantity, FIG. 3(c) is a sectional view of a lens, FIG. 3(d) is a front view of a fixation device, and FIG. 3(e) is an enlarged front view of a light reception section; FIGS. 4(a) to 4(c) are perspective views to show the way of using a photo detector, and FIG. 4(d) is a front view to show the same; FIGS. 5(a) to 5(d) are perspective views to show other examples of belt-like-light generation lenses; FIGS. 6(a) and 6(b) are schematic views to show modified examples (not part of the invention); FIGS. 7(a) to 7(c) are perspective views to show other examples of optical systems; FIG. 8 is an exploded perspective view to show an optical system according to an embodiment which is not part of the invention; FIG. 9(a) is a plan view to show another example of optical element, and FIG. 9(b) is a perspective view to show still another example of the same (not part of the invention); and FIG. 10(a) is a perspective view to show a conventional head unit, and FIG. 10(b) is a view to show light emission areas by the conventional head unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the accompanying drawings, there are shown preferred embodiments of the invention. In FIG. 1, a head unit of a photo detector of an embodiment of the invention comprises a pair of split cases 11 and 12, a fixation device 3, a light shield pipe 4, a cylindrical lens 5, and optical fibers 6 and 7 shown in FIG. 2. Both the split cases 11 and 12 in FIG. 1 are assembled into a head case 1, in which the fixation device 3, the light shield pipe 4 (an example of a shaping element), the cylindrical lens 5 (an example of an optical element), and the tips of the optical fibers 6 and 7 shown in FIG. 2 are housed. The light shield pipe 4 and the cylindrical lens 5 make up an optical system 2 of the invention. The fixation device 3 is provided with three fiber fixing holes 30, 31, and 31. The tip of the light emission optical fiber ( light emission section) 6 is inserted into the center fiber fixing hole 30 and is fixed thereto. The tips of the light reception optical fibers (light reception section) 7 are inserted into the two fiber fixing holes 31 on both sides of the center hole and are fixed thereto. The tip faces of the optical fibers 6 and 7 form an emission face 6a of the light emission section and incidence faces 7a of the light reception section respectively. The base end part of the light emission optical fiber 6 faces a light source and on the other hand, the base end part of the light reception optical fibers 7 is provided with a photoelectric conversion element, forming a known photoelectric switch although not shown. As shown in FIG. 3(a), the fixation device 3, the light shield pipe 4, and the cylindrical lens 5 are placed in the case 1 (FIG. 1) in a state in which they are close to or come in contact with each other in order. The cylindrical lens 5 comprises a first interface 51 and a second interface 52 opposed to each other. The light shield pipe 4 is shaped like a square pipe and the emission face 6a of the light emission optical fiber 6 faces a hollow portion 40 of the light shield pipe 4. Detection light L1 emitted from the emission face 6a passes through the hollow portion 40 of the light shield pipe 4 and is emitted from the first interface 51 of the cylindrical lens 5 through the second interface 52 to a target area A, as indicated by the one-dotted chain lines. On the other hand, reflected light L2 by a detected object or the background in the target area A is incident on the incidence faces 7a of the light reception optical fibers 7 through the first interface 51 of the cylindrical lens 5 from the second interface 52 and is received as indicated by the two-dotted chain lines. A part of the pencil of rays of the detection light L1 passes through the light shield pipe 4 in FIG. 2, whereby the pencil of rays becomes substantially square in transverse section, and the detection light L1 is formed as the elongated detection light L1 substantially shaped like a belt by the one-way light gathering function of the cylindrical lens 5 shown in FIGS. 3(a) and 3(c) and is applied to the target area A. The detection light L1 is reflected by the detected object or the background in the target area A and the reflected light L2 is gathered by the one-way light gathering function of the cylindrical lens 5, is incident on the incidence faces 7a, and is received. The light shield pipe 4 in FIG. 2 is provided with a light decrease wall (light decrease section) 41 for decreasing the quantity of light in the center in a length direction X of the detection light L1 substantially shaped like a belt (length direction in the transverse section of the pencil of rays). If the light decrease wall 41 is not provided, the detection light L1 emitted from the emission face 6a has a strong light quantity in a center C (FIG. 3(b)) of the cross section orthogonal to the optical axis of the detection light L1 and on the other hand, it has a light quantity weakening as it goes to the end parts. In such a light quantity distribution, the light quantity varies largely from one portion of the target area A to another, thus variations in the detection capability occur. In contrast, in the embodiment, the light decrease wall 41 is provided for decreasing the light quantity in the center, so that the light quantity can be made uniform and thus the variations in the detection capability can be suppressed. The light shield pipe 4 in FIG. 2 has a pair of light shield sections 43. Front end faces 42 of the light shield sections 43 are curved to the shape fitted to the first interface 51 of the cylindrical lens 5 and are close to the first interface 51. The light shield sections 43 in FIG. 3(a) prevent light emitted from the emission face 6a to the first interface 51 of the cylindrical lens 5 and specularly reflected thereon from being incident on the incidence faces 7a, whereby stray light can be prevented from being incident on the incidence faces 7a, improving the detection accuracy. The emission face 6a and the incidence faces 7a are disposed at positions distant from the first interface 51 of the cylindrical lens 5. The distance from the emission face 6a to the first interface 51 and that from each incidence face 7a to the first interface 51 are set to substantially the same distance D. The emission face 6a is disposed at the center of the incidence faces 7a. Therefore, in the embodiment, the emission face 6a, the incidence faces 7a, the light shield pipe 4, and the cylindrical lens 5 are disposed substantially symmetrically with a transverse section 53 of the cylindrical lens 5 as the center. As shown in FIG. 2, the light emission optical fiber 6 is made of one optical fiber, while the light reception optical fibers 7 consist of several optical fibers or a large number of optical fibers. As shown in FIGS. 3(d) and 3(e), each incidence face 7a of the light reception optical fibers 7 has a larger number of optical fibers placed on the outside distant from the light emission optical fiber 6, whereby the quantity of light received from the center C of the target area A is suppressed as shown in FIG. 3(b) for making the light reception quantity uniform. That is, the light quantity in the center C is decreased by means of the light decrease wall 41 for making the light quantity uniform, but the light reception quantity may not be made sufficiently uniform. Then, in the embodiment, the light reception quantity is furthermore made uniform by placing the incidence faces 7a as shown in FIGS. 3(d) and 3(e) so that the light quality in the end part can be received more than that in the center C. Next, an example of the use of the detector will be described. As shown in FIG. 4(a), if the position of each workpiece W in a width direction X thereof is undefined with respect to a flow direction Y of the workpiece W, the detector can detect the workpiece W with good accuracy regardless of the position of the workpiece W in the width direction X thereof. Likewise, the detector can detect holes W1 in FIG. 4(b), an edge W2 of a film in FIG. 4(c), and an edge W3 of a label in FIG. 4(d) with good accuracy. Particularly if holes W1 and N different in size exist as in FIG. 4(b), unlike the conventional detectors using spot light for detection, only large holes W1 can be detected without detecting the small hole N or the holes W1 and N can also be distinguished from each other by presetting a threshold value. Of course, the detector of the invention can detect any other object than holes. The invention can be applied not only to detection of the presence or absence of an object, but also to color discrimination of an object to be detected. The head unit gathers the detection light L1 and the reflected light L2 in FIG. 3(a) through one cylindrical lens 5 and forms belt-like detection light. Therefore, the head unit is miniaturized as compared with the conventional head unit with a large number of optical fibers arranged in a row. Moreover, emitted light and received light are gathered through one cylindrical lens 5, so that a manufacturing error is hard to occur in the optical system and thus the manufacturability of the head unit is improved. By the way, the embodiment uses the bar-like cylindrical lens 5 as the lens, but the lens may be a plate-like lens 5A as shown in FIG. 5(a) or a plate-like lens 5B as shown in FIG. 5(b). As shown in FIG. 2, the embodiment uses the lens 5 having the light gathering function only in Y direction of X and Y directions orthogonal to each other in the transverse section of the pencil of rays (Y direction which is orthogonal to the length direction in the transverse section of the pencil of rays). However, in the second aspect of the invention, a pencil of rays substantially shaped like a belt may be formed and therefore the light gathering functions (light gathering degrees) relative to the two directions X and Y may differ. For example, a bar-like lens 5C shown in FIG. 5(c) or a bar-like lens 5D shown in FIG. 5(d) can also be adopted. The bar-like lens 5C in FIG. 5(c) has light gathering functions relative to the two directions X and Y and the light gathering degree relative to the Y direction is large as compared with that relative to the X direction. The bar-like lens 5D in FIG. 5(d) has a light gathering function relative to the Y direction and shows a divergence function relative to the X direction. By the way, the conventional detection head in FIG. 10(a) emits detection light from a plurality of light emission optical fibers 102, so that adjacent light emission areas A1, A2, and A3 overlap each other as shown in FIG. 10(b), thus it is feared that the detection accuracy may be degraded. In contrast, in the embodiment, one emission face 6a is set as shown in FIG. 2, thus the detection accuracy can be improved. In the embodiment, the emission face 6a is placed at the center of the fixation device 3 in FIG. 3(a) and the incidence faces 7a are placed on both sides of the emission face 6a. Thus, if a distance P1 to a detected object is near, light reception areas provided by the two light reception faces 7a do not overlap, while if a distance P2 to a detected object is far, light reception areas provided by the two light reception faces 7a overlap. Generally, if the distance is near, the light quantity increases and if the distance is far, the light quantity decreases. Thus, in the embodiment, if the distance is near, the object is detected in the range in which the light reception areas do not overlap, while if the distance is far, the light reception areas are made to overlap, whereby a more light quantity can be obtained. Therefore, in the embodiment, even if the distance P1 or P2 changes a little, change in the light reception quantity lessens and the fear of erroneous detection lessens. In the embodiment, the incidence faces 7a are placed on both sides of the emission face 6a, but the invention does not limit placement of the light emission section and the light reception section. For example, the incidence faces 7a may be placed coaxially surrounding the emission face 6a. In the embodiment, the light shield pipe 4 and the light shield sections 43 are provided. The embodiment uses one lens 5. However, in the invention, a lens cover 54 may be provided aside from the lens 5 as shown in FIG. 7(a) or two or more lenses 5 and 5E may be provided as optical elements as shown in FIG. 7(b) and 7(c). FIG. 8 shows an embodiment which is not part of the present invention. In this embodiment, a shaping element comprising a light shield plate 4A formed with a through-hole 49 shaped like a groove (slit) and a convex lens 5F make up an optical system 2. In the embodiment, a part of a pencil of rays emitted from an emission face 6a passes through the through-hole 49, whereby it is shaped substantially like a square and shaped detection light L1 is gathered in X and Y directions through the convex lens 5F and is emitted to a target area. Reflected light L2 in the target area passes through the convex lens 5F and the through-hole 49 and is incident on light reception faces 7a. In the embodiment, the light gathering functions of the convex lens 5F are set to the same with respect to the X and Y directions. However, in the embodiment, a cylindrical lens can also be used in place of the convex lens 5F. In the embodiment in FIG. 8, the light shield plate 4A may be placed ahead (Z) of the lens 5F. The above embodiments use lenses as optical elements having the light gathering functions. However, in the invention, a concave mirror 5G having a cylindrical face may provide an optical element as shown in FIGS. 9(a) and 9(b) in place of the lens. As described above, according to the invention, the optical system for shaping the light from the light emission section into a form substantially shaped like a belt and gathering the light in the direction orthogonal to the length direction for generating detection light substantially shaped like a belt is placed ahead of the light emission section and the light reception section. Thus, the light emission and reception head unit having a detection area substantially shaped like a belt such as a shape like a line or a belt can be miniaturized. Since the detection area can be made elongated by the optical element, the detection accuracy is improved. According to the invention, the belt-like-light generation lens may be placed ahead of the light emission section and the light reception section. Thus, the light emission and reception head unit having a detection area substantially shaped like a belt such as a shape like a line or a belt can be miniaturized. Since the detection area can be made elongated by the belt-like-light generation lens, the detection accuracy is improved. Further, if light is gathered through one belt-like-light generation lens, a manufacturing error is hard to occur in the optical system and thus the manufacturability of the head unit is improved. If the optical system is placed substantially symmetrically with the transverse section of the belt-like-light generation lens as the center, the detectable distance range is widened. As the light shield section is provided for preventing stray light from being incident on the light reception section, the detection accuracy is furthermore improved. If the light decrease section is provided for decreasing the quantity of light in the center in the length direction of detection light substantially shaped like a belt, the light quantities can be made uniform, so that the variations in detection capability can be suppressed.

Claims: A head unit of a photo detector for irradiating a target area (A) with detection light (L1) having a pencil of rays having a substantially elongate transverse section and receiving light (L2) reflected in the target area (A), said head unit comprising: at least one light generation lens (5) having different light gathering functions relative to two directions orthogonal to each other in the transverse section of the pencil of rays for generating detection light having a substantially elongate transverse section; a light emission section (6) for emitting light to the target area (A) via said lens (5); and a light reception section (7) for receiving the light (L2) reflected in the target area (A) and incident on said light reception section (7) through said lens (5) , characterized by a pair of light shield sections (43) for preventing light emitted from said light emission section (6) to the light generation lens (5) and specularly reflected thereon from being incident on said light reception section (7). The head unit as claimed in claim 1, further comprising a shaping element (4) for allowing a part of the pencil of rays of the light to pass through and for shaping the transverse section form of the pencil of rays into a form substantially shaped like a square. The head unit as claimed in claim 2, further comprising a light decrease section (41) for decreasing the quantity of light in the center in a length direction in the elongate transverse section of the pencil of rays, and wherein said shaping element (4) is a light shield pipe having a square shape, said light shield pipe (4) having said light decrease section (41) and said pair of light shield sections (43). The head unit as claimed in claim 1 or 2, further comprising a light decrease section (41) for decreasing the quantity of light in the center in a length direction in the elongate transverse section of the pencil of rays. The head unit as claimed in claim 3 or 4, wherein said light decrease section (41) and said pair of light shield sections (43) are integrated with each other. The head unit as claimed in anyone of claims 1 to 5, wherein said light emission section (6) is so arranged that it emits the detection light (L1) from a first interface (51) of said light generation lens (5) through a second interface (52) of said light generation lens (5) to the target area (A); and wherein said light reception section (7) is so arranged that it receives reflected light (L2) incident on said light reception section (7) through the first interface (51) of said light generation lens (5) from the second interface (52). The head unit as claimed in claim 6, wherein front end faces (42) of the light shield sections (43) are curved to the shape fitted to the first interface (51) of the lens (5) and are close to the first interface (51). The head unit as claimed in claim 6 or 7, wherein an emission face (6a) of said light emission section (6) and an incidence face (7a) of said light reception section (7) are disposed at positions distant from the first interface (51), and wherein a distance from the emission face (6a) to the first interface (51) and a distance from the incidence face (7a) to the first interface (51) are set to substantially the same distance. The head unit as claimed in any one of claims 1 to 8, wherein said light generation lens (5), said light emission section (6), and said light reception section (7) are housed in one case (1). The head unit as claimed in claim 9, wherein a pair of split cases (11, 12) are assembled into said case (1), and both ends of said lens (5) have respective protrusions which correspond to an inner wall of said pair of split cases (11, 12). The head unit as claimed in any one of claims 1 to 10, wherein a pair of light reception sections is provided as said light reception section (7), and wherein said light emission section (6) is disposed between said pair of light reception sections (7). The head unit as claimed in claim 11, wherein each of said light reception sections comprises a plurality of optical fibers, and wherein a larger number of optical fibers is placed on the outside distant from said light emission section (6). The head unit as claimed in claim 11 or 12, wherein each of said light reception sections has eight optical fibers, wherein three optical fibers are placed on the light emission section (6) side and five optical fibers are placed on the outside distant from said light emission section (6). The head unit as claimed in any one of claims 12 and 13, wherein said plurality of optical fibers of said pair of light reception sections are bundled together in respective groups at a base end part of said light reception section (7). The head unit as claimed in any one of claims to 14, wherein said light emission section (6), said light reception section (7), said pair of light shield sections, and said at least one light generation lens (5) are placed substantially symmetrically with respect to a plane (53) which is perpendicular to said target area (A) and said light generation lens (5). The head unit as claimed in any one of claims 1 to 15, wherein said light emission section (6) and said light reception section (7) are fixed to one fixation device (3).

Inventors: FUKUMURA KOJI, FUKUMURA, KOJI, Fukumura, Koji, Keyence Corporation
Applicants: KEYENCE CO LTD, KEYENCE CORPORATION
Application year: 1999
Main classification: G01N21
IPC codes: G02B6, H01L31, G02B3