Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1999-09-20
2003-03-04
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559330, C250S559290
Reexamination Certificate
active
06528808
ABSTRACT:
TECHNICAL FIELD
This invention relates to a multiple transmission-type photoelectric sensor for sensing a plurality of objects at one time, a single transmission-type photoelectric sensor capable of being applied particularly to a multiple transmission-type photoelectric sensor, and a photoelectric sensing method.
BACKGROUND ART
Available as one example of a multiple transmission-type photoelectric sensor is a wafer sensor used in a semiconductor-wafer manufacturing process to check semiconductor wafers to determine whether or not they are present, monitor the wafers and verify the number thereof on a lot-by-lot basis.
Sensors described in the specifications of Japanese Patent Publication No. 6-11070 and Japanese Utility Model Application Laid-Open No. 5-66987 are examples of wafer sensors. The wafer sensors described in this literature include a light-projecting element and a photoreceptor element forming a pair and disposed so as to oppose each other. A multiplicity of these light-projecting and photoreceptor elements are inserted between wafers held in a wafer cassette at regular intervals in such a manner that the wafers will be sandwiched by the pairs of light-projecting and photoreceptor elements. A pair of the light-projecting and photoreceptor elements sandwiching a wafer constructs a transmission-type photoelectric sensor. Light projected from the light-projecting element is blocked if a wafer is present but is received by the corresponding photoreceptor element in the absence of a wafer.
Since a semiconductor wafer is opaque, its absence or presence can be sensed on the basis of whether or not the projected light is blocked, as described above. In recent years, transparent or semi-transparent wafers that rely on quartz glass, sapphire glass, liquid-crystal glass and silicon-carbide glass have come to be used for a variety of applications. These transparent or semi-transparent wafers cannot be sensed by, or are difficult to sense by, the above-mentioned wafer sensor. The reason for this is that a transparent wafer transmits most of the projected light from the light-projecting element so that the projected light reaches the photoreceptor element with little attenuation. The difference in amount of light received by the photoreceptor element when a transparent wafer is and is not present is very small and is difficult to identify. In addition, extraneous light and a change in the characteristics of the light-projecting and photoreceptor elements due to temperature are not negligible.
A wafer sensor that is applicable to both transparent and opaque wafers is illustrated in the specification of Japanese Patent Application Laid-Open No. 6-77307. This wafer sensor includes a first element having a light-emitting surface and a photoreceptor surface, and a second element having a photoreceptor surface, the elements being disposed so as to oppose each other. A wafer is inserted between the first and second elements. For a wafer that is opaque, light projected from the first element is blocked by the wafer if the wafer is present. If the wafer is absent, the projected light is received by the second element. In the case of a transparent wafer, light projected from the first element and reflected by the wafer (if the wafer is present) is received by the photoreceptor surface of the first element. If the wafer is absent, light does not impinge upon the photoreceptor surface of the first element. This is premised on the fact that whether the wafer is a transparent wafer or an opaque wafer is known beforehand. The photoreception signal of the first element and the photoreception signal of the second element are switched, depending upon the type of wafer, before being applied to a discriminating circuit.
This wafer sensor requires the first element having the light-emitting and photoreceptor surfaces. In the case of a transparent wafer, the sensor receives the light reflected from the wafer and therefore is readily influenced by the surface of the wafer. The wafer type, i.e., transparent or opaque, must be known in advance.
In the wafer sensors of all of the above-mentioned types, a light-projecting (light-emitting) element and a photoreceptor element must be inserted in the gaps between wafers. There has been a tendency in recent years for the gaps between the multiplicity of wafers held in the wafer cassette to be made smaller. There is a limit upon the extent to which the thickness of the light-projecting and photoreceptor elements and the thickness of the members for holding these elements can be reduced.
There are occasions where the wafers in a semiconductor process become charged with static electricity. If this static electricity discharges through electrically conductive portions of the light-projecting and photoreceptor elements inserted between the wafers, there is the danger that this may lead to erroneous detection and destruction of the light-projecting and photoreceptor elements.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a transmission-type photoelectric sensor, multiple transmission-type photoelectric sensor and photoelectric sensing method capable of sensing both opaque and transparent bodies (inclusive of semi-transparent bodies).
Another object of the present invention is to provide a structure whereby a sensing portion inserted between objects to be sensed can be made as thin as possible.
A further object of the present invention is to provide a structure whereby the influence of static electricity that has charged an object to be sensed can be made as small as possible.
Still another object of the present invention is to provide a structure whereby the number of light-projecting and photoreceptor elements can be made as small as possible.
A multiple transmission-type photoelectric sensor according to the present invention is defined as follows when expressed all-inclusively: Specifically, a multiple transmission-type photoelectric sensor according to the present invention has a plurality of sensing arms provided in spaced-apart relation on a sensor case so as to extend outwardly of the case, and a plurality of light-projecting elements and a plurality of photoreceptor elements provided inside the sensor case, one light-projecting element, one photoreceptor element or one pair of the light-projecting and photoreceptor elements corresponding to each sensing arm, a distal end of each sensing arm being provided with at least one of a first deflecting member for directing projected light from the corresponding light-projecting element toward a neighboring sensing arm and a second deflecting member for directing projected light from the neighboring sensing arm toward the corresponding photoreceptor element.
In one embodiment, one pair of the light-projecting and photoreceptor elements corresponds to each sensing arm, and each sensing arm is provided with the first deflecting member and the second deflecting member. In another embodiment, one light-projecting element or one photoreceptor element corresponds to each sensing arm, the distal end of the sensing arm that corresponds to the light-projecting element is provided with the first deflecting member, and the distal end of the sensing arm that corresponds to the photoreceptor element is provided with the second deflecting member.
In any case, the space between two neighboring sensing arms is a sensing area, projected light from the light-projecting element of one sensing arm reaches the neighboring other sensing arm by traversing the sensing area at least one time (two or more times depending upon the mode) and is received by the photoreceptor element of the one sensing arm or of the other sensing arm. By subjecting the photoreception signal of the photoreceptor element to level discrimination, at least the absence or presence of an object in the sensing area is determined.
In accordance with the present invention, a plurality of sensing arms are provided. As a result, a plurality of sensing areas are established and sensing operations can be performed simultaneously in these plu
Foley & Lardner
Le Que T.
Luu Thanh X.
Omron Corporation
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