A PHOTOELECTRIC SENSOR

Abstract: A photoelectric sensor comprises a thin plate-shaped optical body (1), a circuit block (4) and a tubular casing (2) for incorporating therein the optical body and the circuit block. A signal light incoming through a transparent protector of the casing is reflected upon a first reflective mirror (1c) of the optical body. Following this first reflection, a second reflection is made upon a second reflective mirror (41a) thereof. The light having passed through a light collecting lens is received by a photoelectric converting element (4a) and converted into electric signals for output. Since the optical body comprises a plurality of reflective surfaces, an optical path up to the photoelectric converting element can be incorporated compactly within the thin plate-shaped optical body.

Description: This invention relates to a photoelectric sensor comprising a light collecting system and a light receiving system. The photoelectric sensor enables a non-contact detection of persons or objects, so that it is used to detect any objects to be conveyed in various automated machines or conveyer lines, and any person's approach to an automatic door or the like. In Fig. 13 there is shown a section view of a conventional photoelectric sensor wherein a convex lens is fixed in a circular opening formed on a front side of a casing. Disposed on a focal point of the convex lens is a photoelectric element comprising a light emitting element such as a light emitting diode and a light receiving element such as a photo-transistor. Fixed upon an inner surface of a casing are a light driving circuit, a signal amplifying circuit, an operation indicating lamp, a variable resistor and other parts so as not to hinder the optical path between the convex lens and the photoelectric element. All of the aforesaid components are electrically connected to each other. An electric wire connected to an input terminal and an output terminal is connected to a device outside the casing. Referring to Fig. 13, symbol A is a convex lens for light collection which is disposed on a front side of a casing B. Numeral 61 is a photoelectric element disposed on a focal point of the convex lens A. Numeral 62 is a wiring substrate, numeral 63 represents a plurality of electronic parts disposed upon the wiring substrate 62 and numeral 64 is an operation indicating lamp. Such a photoelectric sensor can be installed on a certain place by means of brackets screws. In recent years, the structure of the photoelectric sensor becomes more small-sized and more compact to meet users' requirements. Yet there are the following problems hindering the manufacture of a small-sized photoelectric sensor. Firstly, when disposing necessary parts upon the inner wall of the casing of the photoelectric sensor, an assembler is forced to insert such tools as a driver, pincettes, soldering tool or the like into the interior of the casing. Accordingly, as the casing becomes smaller, assembling becomes more cumbersome. Thus, to make the photoelectric sensor smaller is contradictory to a better efficiency of assembling. Secondly, since a convex lens is adapted for a light collecting means, a conically enlarged space must be formed in an optical path toward the photoelectric converting element. More particularly, in order to enhance the performance of the photoelectric sensor, it is desirable to increase the light incoming volume by enlarging a caliber of the convex lens and to minimize the influence of any outer disturbing light by extending a focal distance of the convex lens. Therefore, it is needed to dispose a lens having a larger caliber and a longer focal distance, so that a larger conical space must be formed. In this regard, to make the photoelectric sensor smaller is contradictory to the betterment of the optical properties. Further, one of the defects of the conventional photoelectric sensor is inconvenient in handling. Since it is large-sized, it is easily touched by persons or objects, thereby an optical axis is biassed and it causes malfunction. Finally, when some dusts or oily matters will be stuck to a body of the photoelectric sensor, cleaning is not easy. It is therefore a general object of the invention to provide a compact photoelectric sensor which brings a good fabricability, a super optical performance and a suitable operability. The photoelectric sensor according to this invention comprises: a transparent optical body comprising a semicrescent-shaped section having a circular flattened objective surface as a front surface and a circular convex surface as a rear surface; a circuit block behind the transparent optical body; a transparent protector in front of said transparent optical body; the optical body being, on a central part of the front surface, provided with a first recess having about one-third diameter of the front surface, while being, on a central part of the rear surface, provided with a second recess having a convex bottom and a smaller diameter than said first recess, said second recess forming a light collecting lens opposed to a photoelectric converting element; a concave bottom of the first recess being formed as a second reflective mirror by a vacuum evaporating plating means; a surface other than said second recess of the rear surface being formed as a first reflective mirror by a vacuum evaporating plating means, and a periphery of the rear surface having a skirt member and the first reflective mirror being provided with a light collecting lens for transmitting a luminous flux; the circuit block being provided, on its front surface, with the photoelectric converting element and an operation indicating lamp and, and a periphery of said circuit block being directed to the skirt member. Still further, the photoelectric converting element by known photoelectric sensors is usually provided with a metal evaporating plating thereupon in order to prevent any error operation that may be caused by electromagnetic radiating noises occuring e.g. by starting an inverter motor, but its defect is that the light transmitting rate is deteriorated. With respect to claim 2 a photoelectric sensor is further known which comprises a light collecting block having a reflective mirror, formed on a central part of the inner surface of a light transmitting window, and a concave mirror including a light passing portion and arranged opposite to the concave mirror (US-A-4 792 685). The photoelectric sensor comprises further an electronic circuit block having a photoelectric element positioned on a light collecting point of the light collecting block, a plurality of electronic components and a wiring substrate. In order to prevent invasion of any harmful outer disturbing light or any electric noise, the inner surface of the light collecting block excluding the light transmitting window and an indicating light transmitting window is provided with a membran formed by metal evaporation or coating. It is a further object of the invention, to provide a photoelectric sensor, which is free from any influence of the electromagnetic radiating noises. This object is achieved according to the invention by the features as directed in claim 2. The invention will now be described with reference to the accompanying drawings. In the drawings: Figs. 1 to 4 show a first embodiment of a photoelectric sensor according to the invention. Fig. 1 is a vertical section view of the photoelectric sensor. Fig. 2 is a front view thereof. Fig. 3 is a side view thereof. Fig. 4(a) is a side view of an optical body. Fig. 4(b) is a front view thereof. Fig. 4(c) is a section view taken along line c-c in Fig. 4(b). Fig. 4(d) is a rear view thereof. Figs. 5 to 7 show a second embodiment of a photoelectric sensor according to the invention. Fig. 5 is a vertical section view of the photoelectric sensor. Fig. 6 is a front view thereof. Fig. 7 is a side view thereof. Figs. 8 to 12 show a third embodiment of a photoelectric sensor according to the invention. Fig. 8 is a vertical section view of the photoelectric sensor. Fig. 9 is a front view thereof. Fig. 10 is a side view thereof. Fig. 11 is a rear view thereof. Figs. 12(a) and 12(b) are perspective views of a first shielding member and of a second shielding member respectively. Fig. 13 is a vertical section view of a conventional photoelectric sensor. Preferred embodiments of this invention will now be described with reference to the accompanying drawings. Figs. 1 to 4 show a first embodiment according to the invention. Numeral 1 is a transparent resinous optical body having a thin plate shape. Numeral 2 is a resinous casing having an opening side. An outer surface of the casing 2 is provided with a screw thread portion 2a. Numeral 2b is a ring-shaped stopper integrally fixed with the casing 2 and formed immediately behind an objective surface. The stopper 2b is, on its inner surface, provide with a groove to insert therein a locking nail 3a of a transparent resinous protector 3. The protector 3 is a disc type, which is disposed in the opening of the casing 2. Numeral 4 is a circuit block which is disposed so as to oppose to a rear surface of the optical body 1. Mounted upon a surface opposed to the optical body 1 are a photoelectric converting element 4a and an operation indicating lamp 4b, while mounted upon a rear surface with respect to the optical body 1 is a plurality of electronic parts 4c. Numeral 5 is an epoxy resinous material filled between the circuit block 4 and the bottom of the casing 2 to protect the circuit block from water, shaking and humidity. Numeral 6 is a lock nut engageable with a screw thread portion 2a. The photoelectric sensor is fixed on a panel 8 which is clamped between the stopper 2b, a rubber washer 7 and the lock nut 6. Numeral 9 is an annular rubber packing which is inserted between the protector 3 and the casing 2. Numeral 10 is a lead wire for input/output to be connected to the circuit block 4. The construction of the optical body 1 will now be described in connection with Figs. 4(a), 4(b), 4(c) and 4(d). The transparent resinous optical body 1 has a semicrescent-shaped section and a diameter of 20 mm. Numeral 21 is a circular flattened objective surface which is formed toward an object to be detected. (The objective surface 21 has a diameter of 18 mm.) In case of detecting an object existing within about 1 meter distant from the objective surface 21 it is preferably formed as a gently convex surface. Numeral 31 is a circular convex surface having a diameter of 18 mm(R=13.4 mm, aspherical). The circular convex surface 31 is opposed immediately to a photoelectric converting element 4a. As illustrated clearly in Figs. 4(b) and 4(c), formed upon a central part of the objective surface 21 is a first recess 41 having a concave surface with a diameter of 7mm (R=7.7mm) which is nearly equivalent to one-third of the circular convex surface 31. Further, the first recess 41 is, upon its concave bottom surface, provided with a second reflective surface 41a which is formed by a vacuum evaporating plating process. Numeral 51 is a second recess formed on a central part of the circular convex surface 31 so as to oppose to the first recess 41. A convex bottom surface of the second recess 51 has a slightly smaller diameter than a bottom surface of the first recess 41. The ratio of both bottom surfaces is 15 : 1. The convex surface of the second recess 51 constitutes a light collecting lens 51a. The photoelectric converting element 4a of the circuit block 4 is directly faced or fitted to the second recess 51. Numeral 1a is a skirt (about 3 mm in height) formed upon a circumference of the circular convex surface 31. Numeral 1b is an opening formed on the circular convex surface 31 in order to radiate a luminous flux of the operation indicating lamp 4b through the objective surface 21. The opening 1b has a convex bottom surface. Alternatively, it may be formed as a Fresnel surface. In this case the radiated light becomes a parallel one, that is visible from a far distance. Numeral 1c is a first reflective surface formed upon the circular convex surface 31 by means of a vacuum evaporating plating process. According to this embodiment, the photoelectric sensor has an outer diameter of 20 mm and a thickness of about 14mm. An operation of this embodiment will be described. A signal light incoming from the circular objective surface 21 of the optical body 1 through the protector 3 is reflected upon the first reflective surface 1c and transferred to the second reflective surface 41a. Then, a second reflection occurs. Due to this second reflection, the light passing light collecting lens 51 is collected upon the photoelectric converting element 4a, and converted into electric signals for output. Any variation of the incoming light volume is immediately converted electric signals, so that any persons or object existing in an optical path before the protector 3 or the objective surface 21 is detected. Since the optical body 1 comprises the first reflective surface 1c and the second reflective surface 41a, an optical path to the photoelectric converting element 4a from a circular objective surface of the convex lens A as shown in a conventional photoelectric sensor in Fig. 13 can be formed compactly in a folded state within the thin plate-shaped optical body 1. The light from the operation indicating lamp 4b as a light emitting diode is radiated to the objective surface 21 of the optical body 1 through the light collecting lens means 9. The most part of the electromagnetic noises is intercepted by the metal coating formed on the first reflective surface 1c and the second reflective surface 41a, thereby a plurality of electronic parts 4c on the circuit block 4 can be operated exactly. Thus, both the first reflective surface 1c and the second reflective surface 41a have the function of preventing the electromagnetic radiating noises. The metal coating(not illustrated) is electrically connected to a ground of a power source. A second embodiment of this invention will be described in connection with Figs. 5, 6 and 7. Since the components in the second embodiment have the same numerals as in the first embodiment, their description will be omitted. In the second embodiment, the construction of the casing 2 and the protector 3 slightly differs from that in the first embodiment, and the other construction is the same to the first one. In this embodiment, the whole circumference of the casing 2 is provided with the screw thread portion 2a, but not provided with the stopper 2b. The protector 3 is of a shallow casing type, and its bottom surface is opposed to the objective surface 21 of the optical body 1. The protector 3 is, on its inner circumference, provided with an inner screw thread portion to be engaged with the screw thread portion 2a of the casing. A mounting panel 8 is supported through the washer 7 between a side edge of the protector 3 and the lock nut 6. The function and effects of the second embodiment are the same to those of the first embodiment. In the second embodiment, mounting of the protector 3 to the casing 2 is easier than in the first embodiment. A third embodiment of this invention will be described in connection with Figs. 8 to 12. Since some of the components in the third embodiment have the same numerals as in the previous embodiments, their description will be omitted. Referring to Fig. 8, the casing 2 having one opening side is made of a transparent material capable of cutting any visible light. Inserted in a position opposed to the convex portion 1b of the optical body 1 is an indicating light transmitting member 3b of the optical body 1. Numeral 41b is a first shielding metal disc arranged at the opening of the first recess 41 of the optical body 1, while numeral 51b is a second shielding metal member fitted in the second recess 51. As clearly illustrated in Fig. 12, the first shielding metal disc 41b is a circular one, while the second shielding metal member 51b comprises a cylindrical shape, which has a shielding disc 51c having an aperture 51c1. The light is passed through the aperture 51c1. Due to the second metal member 51b the circuit block 4 is not affected by any electromagnetic radiating noises from a backward and sideward direction. Further, the electromagnetic radiating noises from a front direction are shielded effectively by the first shielding disc 41b, while those from an obliquely forward direction are shielded by the second metal member 51b. The photoelectric sensor according to this embodiment is suitable for various devices that are used in fields filled with electromagnetic radiating noises. As discussed above, any cumbersome manual assembling such as insertion of components into a narrow interior of the casing has completely been removed, so that the photoelectric sensor according to this invention can be mass-produced by means of various robot machines. Thus, the manufacturing cost can be reduced greatly. Further, a conical space upon an optical path is incorporated compactly in the interior of the optical body comprising a semi-crescent-shaped section. Thus, the optical body is formed very thin and small-sized. For example, its thickness is as small as about one-third of a conventional optical body. Accordingly, the small-sized photoelectric sensor according to this invention can be mounted simply on any wall in factories, offices, shops or houses without injuring any aesthetic appearance of the surroundings. Further, since the caliber of the optical body is larger and its focal distance is long, the light incoming volume is increased and any outer disturbing light is not influential. Accordingly, when one photoelectric sensor having the function of a light transmitting device is opposed to another photoelectric sensor having the function of a light receiving device, it is possible to extend its opposing distance greatly. Further, when the photoelectric sensor is of a reflective type, it is possible to extend a distance between the photoelectric sensor and an object to be detected, and to make its detection easier. Still further, the present photoelectric sensor enables a very accurate detection by shielding any outer electromagnetic radiating noises.

Claims: A photoelectric sensor comprising: a transparent optical body (1) comprising a semicrescent-shaped section having a circular flattened objective surface (21) as a front surface and a circular convex surface (31) as a rear surface; a circuit block (4) behind said transparent optical body; a transparent protector (3) in front of said transparent optical body; said optical body (1) being, on a central part of said front surface, provided with a first recess (41) having about one-third diameter of said front surface, while being, on a central part of said rear surface, provided with a second recess (51) having a convex bottom and a smaller diameter than said first recess, said second recess forming a light collecting lens (51a) opposed to a photoelectric converting element (4a); a concave bottom of said first recess (41) being formed as a second reflective mirror (41a) by a vacuum evaporating plating means; a surface other than said second recess (51a) of said rear surface being formed as a first reflective mirror (1c) by a vacuum evaporating plating means, and a periphery of said rear surface having a skirt member (1a) and said first reflective mirror being provided with a light collecting means (1b) for transmitting a luminous flux; said circuit block (4) being provided, on its front surface, with said photoelectric converting element (4a) and with an operation indicating lamp (4b) and the periphery of said circuit block being directed to said skirt member (1a). A photoelectric sensor as claimed in claim 1, wherein said transparent optical body (1) and said circuit block (4) being arranged in a tubular casing (2) having an opening side, to which the transparent protector (3) being fitted, and wherein, in order to shield any outer electromagnetic radiating noises, a circular metal disc as a first shielding member (41b) and a cylindrical metal body as a second shielding member (51b), in which a shielding disc (51c) with an aperture (51c1) is arranged, are disposed in said first recess (41) and said second recess (51), respectively. A photoelectric sensor as claimed in claim 2, wherein said casing (2) is, on its outer circumference, provided with a screw thread portion (2a) and a stopper (2b) engaged with a lock nut (6), thereby a mounting panel (8) is supported between said lock nut (6) and said stopper (2b). A photoelectric sensor as claimed in claim 2, wherein said casing (2) is provided with a screw thread (2a) on its whole circumference, the protector (3) is of a shallow casing type comprising a bottom and a cylindrical wall part, on the inner circumference of this latter a screw thread is provided, which is engaged with the screw thread (2a) of the casing (2), and wherein a mounting panel (8) is supported between the end of the cylindrical part of the protector (3) and a lock nut (6). A photoelectric sensor as claimed in one of claims 2 to 4, wherein a resinous material (5) is filled in a space between a bottom of said casing (2) and said circuit block (4).

Inventors: YAMAKAWA, MASAMI C/O AISENS CO., LTD.
Applicants: AISENS CO. LTD.
Application year: 1989
Main classification: G01V9
IPC codes: H01L31, G01V8, G02B17, G02B27, G08B13