JP2006019939A - Photoelectric sensor and water detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric sensor and a wafer detector reliably detecting a light transmissive object to be detected. <P>SOLUTION: In a non-detection state, a first threshold Th1 having a large margin is compared with a photoreceptive volume level to be successively taken in. With a case when the photoreceptive volume level is smaller than the first threshold Th1 as a trigger, the detection of a wafer W is determined, based on the comparison with a second original threshold Th2. And the first and second thresholds Th1, Th2 are set, on the basis of the average value of 255 or 235 photoreceptive volume levels taken in immediately before. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a so-called transmissive photoelectric sensor and a wafer detection apparatus.

Conventionally, the light projecting means and the light receiving means are arranged opposite to each other with a predetermined detection area interposed therebetween, and the received light amount level at the light receiving means that changes according to the light shielding state of the detected object existing in the detection area There is a so-called transmissive photoelectric sensor that detects the detected object based on a comparison with a threshold value (see Patent Document 1 below). Such a photoelectric sensor may be used for detecting a glass wafer in a manufacturing process of a glass wafer having light transmittance, for example. The light reception level when the glass wafer is in the detection area (hereinafter referred to as “detection state”) is lower than the light reception level when the glass wafer is not within the detection area (hereinafter referred to as “non-detection state”). To do. Therefore, the threshold value is set between these received light amount levels.
JP 2003-87107 A

  However, when the object to be detected has light transmittance like a glass wafer, the difference between both received light amount levels in the detection state and the non-detection state is extremely small. For this reason, if a situation occurs in which the light reception level at the light receiving means is lowered even in the non-detection state, even if it is still in the non-detection state, the light reception level is detected below the threshold value. There was a risk that it was erroneously determined to be in a state. For example, a piece of glass wafer moving on the production line may fall to the front of the light receiving means, and the above problem occurs in such a case.

  The present invention has been completed based on the above-described circumstances, and an object thereof is to provide a photoelectric sensor and a wafer detection device capable of more reliably detecting a light-transmitted object to be detected. To do.

As means for achieving the above object, a photoelectric sensor according to the invention of claim 1 is characterized in that a light projecting means for emitting light to a predetermined detection area where a light-transmitting object to be detected moves, and the light projection A light receiving means arranged so as to be able to receive light emitted from the means and transmitted through the detection area, a threshold setting means for setting a threshold value, a received light amount level at the light receiving means that changes depending on the presence of the detected object, and Compared with the threshold value set in the threshold value setting means, when the received light amount level is equal to or lower than the threshold value, it is determined that the detected object is detected, and when the detected light level exceeds the threshold value, the detected object level is determined. A non-detection state determination unit, wherein the threshold value setting unit is configured to detect the amount of light received in the non-detection state when the determination result of the determination unit is in the non-detection state. Before level and said detection area While setting a first threshold value between the received light amount level when the edge of the detection object is located, on the condition that the determination result in the determination means has changed from the non-detection state to the detection state, A second threshold value is set between a received light amount level in the non-detection state and a received light amount level when a portion other than the edge of the detected portion is located in the detection region.
The “detectable object having optical transparency” is not limited to a transparent object such as a glass object, but also includes a translucent object such as a silicon object.

  According to a second aspect of the present invention, in the photoelectric sensor according to the first aspect, in the non-detection state, a light reception amount level at the light receiving unit is read, and an average value of a plurality of light reception amount levels read within a predetermined period. The threshold value setting means sets the first and second threshold values based on the average value obtained by the average value measurement means.

  According to a third aspect of the present invention, in the photoelectric sensor according to the second aspect, when the second threshold value is set, the predetermined period is a period before a certain period immediately before the non-detection state is changed to the detection state. It is characterized by being.

  According to a fourth aspect of the present invention, in the photoelectric sensor according to any one of the first to third aspects, the determination unit has a predetermined period from a time point when a light reception amount level at the light reception unit falls below the first threshold value. It has a invalidating means for invalidating the comparison operation with the second threshold value.

  According to a fifth aspect of the present invention, in the photoelectric sensor according to any one of the first to fourth aspects, in the comparison operation with the second threshold, the light receiving amount level at the light receiving unit is the first level. It is determined that it is the non-detection state on condition that a state exceeding 2 thresholds has continued for a predetermined time.

A wafer detection apparatus according to a sixth aspect of the present invention is a wafer detection apparatus for detecting a dimension of a wafer as a detected object having a light transmission property by moving in a predetermined detection region. 5. A photoelectric sensor according to claim 5, and a dimension detecting means for detecting a dimension of the wafer based on a duration time determined to be in a detection state by the determining means of the photoelectric sensor.
In addition to the configuration for measuring the dimension value of the wafer based on the duration time, the “dimension detection means” compares the duration time with a reference time to determine whether the dimension of the wafer matches a predetermined reference dimension. The structure to detect may be sufficient.

<Invention of Claim 1>
In general, in a so-called transmissive photoelectric sensor formed by arranging a light projecting unit and a light receiving unit to face each other, compared to a case where a portion other than the edge portion is located in the detection region of the detected object having light transmittance, When the edge portion is located, the light receiving level at the light receiving means is greatly reduced.
Therefore, in this configuration, for example, in the non-detection state where there is no detection object in the detection region, the light reception level at the light receiving means is detected in the detection region in the detection region with the light reception level (V1) in the normal non-detection state. It compares with the 1st threshold value set between the received light quantity level (V2 <V1) when the edge of an object is located. And when the edge part of a to-be-detected object is located in a detection area, the determination means will determine with a detection state by the light-receiving-amount level falling below the said 1st threshold value. Thereafter, the received light amount level at the light receiving means is the received light amount level (V1) in the normal non-detection state and the received light amount level when a portion other than the edge of the detected portion is located in the detection region. The determination is made in comparison with the second threshold value between (V3. V2 <V3 <V1). That is, in the non-detection state, the second threshold value with a relatively small margin is compared with the first threshold value having a relatively large margin, and on the condition that the comparison result has changed from the non-detection state to the detection state. The comparison operation is shifted to.
Therefore, for example, in the non-detection state, if a detected object fragment or the like is present in the detection region and the light reception level at the light receiving unit is slightly reduced, the light reception level at the light receiving unit is simply The risk of erroneous detection can be suppressed compared to a configuration in which detection is performed by comparison with only a threshold corresponding to one threshold.

<Invention of Claim 2>
According to this configuration, since the first and second threshold values are set to values corresponding to changes in the average value obtained by the average value measuring means, the received light amount level due to element degradation or the like is changed over time. Even in the case of changing to, the first and second threshold values are set to appropriate values in accordance with the change, and the influence due to the temporal change in the received light amount level can be eliminated.

<Invention of Claim 3>
When changing from the non-detection state to the detection state, the received light amount level at the light receiving means changes greatly so as to be lower than the first threshold value. Accordingly, it is not preferable to set the second threshold based on the average value of the received light amount level at this time. Therefore, in this configuration, the second value is calculated based on the average value of the plurality of received light amount levels at a timing before a certain period (period in which the received light amount level changes greatly) immediately before the average value measuring unit changes from the non-detected state to the detected state. The threshold is set.

<Invention of Claims 4 and 5>
In the comparison operation with the second threshold value, since the margin between the second threshold value and the received light amount level at the light receiving means is small, for example, erroneous detection is performed by a minute level change due to noise (for example, internal reflection of the detected object). May cause. Therefore, in the configuration of claim 4, the comparison operation in the determination unit is invalidated for a predetermined period from the time when the received light amount level in the light receiving unit falls below the first threshold value. Further, in the configuration of claim 5, it is determined that the non-detection state is not performed when the received light amount level exceeds the second threshold on a single occasion.

<Invention of Claim 6>
By applying the invention according to any one of the first to fifth aspects, the dimensions of the wafer can be accurately detected.

An embodiment of the present invention will be described with reference to FIGS.
In the present embodiment, as shown in FIG. 1, for example, a wafer detection for detecting a light-transmitting wafer W (for example, a glass wafer or a silicon wafer; an object to be detected) transported by a U-shaped transport arm 11. The present invention is applied to the apparatus 10.

1. Hardware Configuration As shown in FIG. 2, the wafer detection apparatus 10 according to the present embodiment includes a sensor main body 14 including a light projecting element 12 (for example, an LED and a laser diode), a light receiving element 13 (for example, a photodiode and a phototransistor), and the like. The optical fibers F1 and F2 are derived from the above so-called fiber sensor. Specifically, the end face on the sensor body 14 side of the optical fiber F1 is abutted against the front surface of the light projecting element 12, and the light from the light projecting element 12 is transmitted and arranged on the passage path side of the wafer W. The light is emitted from the tip surface. The light projecting element 12 emits light when a drive current is applied from the light projecting element driving circuit 15. Therefore, the optical fiber F1 and the light projecting element 12 correspond to the “light projecting means” of the present invention.

  On the other hand, the end face of the optical fiber F2 is abutted against the front surface of the light receiving element 13 on the sensor main body 14 side, and plays a role of guiding light incident from the front end face disposed on the passing path side of the wafer W to the light receiving element 13. . The light receiving element 13 outputs a light receiving signal at a level corresponding to the amount of received light (light receiving amount), is A / D converted by an A / D converter (not shown), and is taken into the control circuit 16. Therefore, the optical fiber F2 and the light receiving element 13 correspond to the “light receiving means” of the present invention. The control circuit 16 is connected to the light projecting element drive circuit 15, the volatile memory 17 (for example, RAM), the nonvolatile memory 18 (for example, EPPROM), and the output circuit 19, respectively.

  And the front-end | tip parts F1a and F2a of each optical fiber F1 and F2 are opposingly arranged so that the passage route of the wafer W may be pinched | interposed vertically, for example. That is, it is used as a so-called transmission type sensor.

2. Software Configuration Now, as shown in FIG. 3, when the wafer W is not in the area opposite to the front ends F1a and F2a of the optical fibers F1 and F2 (hereinafter referred to as “detection area X”) (FIG. 3A) E)), a light reception signal having a high light reception level V1 is output from the light receiving element 13. On the other hand, when the wafer W has completely entered the detection region X (FIG. 3C), the light reception level V2 (slightly lower than the light reception level V1) because the wafer W is light transmissive. For example, a light reception signal of 90% of the light reception level V1) is output. Therefore, as described above, in the configuration in which the second threshold value Th2 is simply set and compared between the both received light amount levels V1 and V2, it is caused by fragments or the like in the non-detection state (FIGS. If the received light amount level temporarily decreases, there is a possibility that the detection of the presence of a wafer may be erroneously detected even though there is no wafer W in the detection region X.

  Here, looking at the displacement of the received light amount level in FIG. 3, when the edge portion of the wafer W is present in the detection region X (FIGS. (B) and (D)), the received light amount level temporarily decreases greatly. (The light reception level V3 at this time is, for example, 50% of the light reception level V1). This is probably because the end face of the wafer W is actually uneven, and light is refracted here.

  Therefore, the control circuit 16 executes the control shown in FIG. First, it is determined whether or not the detection flag is set in S1, and if it is not set (“N” in S1), the light projecting element driving circuit 15 is driven in S2 to cause the light projecting element 12 to emit light, and in synchronization therewith. The light receiving signal is taken in from the light receiving element 13 and stored in the volatile memory 17. Next, in S3, it is determined whether or not a predetermined number (for example, 255) of received light signal data is stored in the nonvolatile memory 18. If 255 are stored (“Y” in S3), the average value of the received light amount level is calculated based on the 255 received light signal data in S4. Specifically, the total received light amount of 255 received light signal data is divided by 255. Then, for example, a value of 75% of the average value is set as the first threshold Th1, and the calculated first threshold Th1 is compared with the currently received light amount level in S5. The first threshold value Th1 is stored in the nonvolatile memory 18. If the previously set first threshold Th1 is already stored in the nonvolatile memory 18, it is rewritten and updated. Accordingly, in this case, the period of capturing 255 received light signals corresponds to the “predetermined period” of the present invention.

  On the other hand, if it is less than 255 (“N” in S3), it is determined in S6 whether or not the first threshold Th1 is already stored in the nonvolatile memory 18, and if not stored (“N” in S6). Return to S1 again. If stored, the first threshold value Th1 stored in the nonvolatile memory 18 is compared with the currently received light amount level in S5. When the received light amount level is larger than the first threshold Th1 (“N” in S5), the process returns to S1 again assuming that there is no wafer W in the detection region X (state in FIG. 3A). On the other hand, when the received light amount level is smaller than the first threshold Th1 (“Y” in S5), the detection flag is set in S7, the first count is started, and the process returns to S1. Here, the first threshold Th1 is smaller than the received light amount level V1 when the entire wafer W is interposed in the detection region X, and is smaller than the received light amount level V3 when the edge portion of the wafer W is interposed in the detection region X. Set to a large value. Therefore, when the currently received light amount level read is smaller than the first threshold Th1, it means that the edge portion of the wafer W has entered the detection region X (the state shown in FIG. 3B).

  Next, when returning to S1, if the detection flag is set (“Y” in S1), the light projecting element drive circuit 15 is driven in S8 to cause the light projecting element 12 to emit light, and light is received in synchronization with it. A light reception signal is taken from the element 13. At this time, the wafer W is in the state shown in FIG. Then, in S9, it is determined whether 255 received light signal data stored in the volatile memory 17 are stored. If 255 signals are stored (“Y” in S9), a predetermined number (for example, 20) of light reception signal data acquired most recently among the 255 light reception signal data currently stored in the nonvolatile memory 18 in S10. The average value of the received light amount level is calculated based on the 235 received light signal data excluding. Specifically, the total received light amount of 235 received light signal data is divided by 235. Then, for example, a value of 90% of this average value is set as the second threshold value Th <b> 2 and stored in the nonvolatile memory 18. If the previously set second threshold Th2 is already stored in the nonvolatile memory 18, it is rewritten and updated. Therefore, in this case, the period for capturing 235 received light signals corresponds to the “predetermined period” of the present invention.

Here, the 255 received light signal data stored in the nonvolatile memory 18 at this time is the time when the received light amount level is lower than the first threshold Th1 in S5, that is, before the change from the non-detection state to the detection state. Is remembered. Of the 20 most recent received light signal data, as shown in FIG. 3, the data is acquired within the time T when the received light amount level greatly changes, and the average value including these should not be calculated. Because.
On the other hand, if it is less than 255 (“N” in S9), if the second threshold Th2 is already stored in the nonvolatile memory 18 in S11 (“Y” in S11), the process proceeds to S12, and if not stored. ("N" in S11) Return to S1.

  Next, in S12, it is determined whether or not the predetermined time t1 has elapsed. If it has not elapsed ("N" in S12), the process returns to S1, and if it has elapsed ("Y" in S12), In S13, the second threshold value Th2 is compared with the currently received light amount level. As described above, as described above, the comparison with the second threshold Th2 is not performed until the predetermined time t1 elapses after the received light amount level falls below the first threshold Th1. This is because the received light amount level V2 when the entire wafer W intervenes (the state in FIG. 3C) is easily affected by noise because the difference from the second threshold Th2 is small.

  Subsequently, when the received light amount level falls below the second threshold Th2 in S13 (“Y” in S13), the second count is started in S14, and if the second count has not passed the predetermined time t2 in S15 ( ("N" in S15)) Return to S1 again. If the received light amount level read in the next light projecting / receiving operation in S8 exceeds the second threshold Th2 (“N” in S13), the second count is cleared in S16 and the process returns to S1. On the other hand, the detection operation is executed for the first time (S17) when the light reception level is below the second threshold Th2 (“Y” in S13) continues for a predetermined time t2 (“Y” in S15). For example, a detection signal is output from the output circuit 19 shown in FIG. 2 or the operation indicator lamp 20 is turned on. The detection flag is cleared when the light reception level exceeds the second threshold Th2 after the detection operation is once executed (FIG. 3D).

3. Effects of the present embodiment (1) According to the present embodiment, in the non-detection state (FIG. 3A), a comparison is made with the first threshold Th1 having a large margin with respect to the sequentially received light amount level. The detection of the wafer W is determined based on the comparison with the original second threshold value Th2 with the fact that it is below the first threshold value Th1 as a trigger. Accordingly, it is possible to prevent erroneous detection due to a slight fluctuation in the light reception level in the non-detection state.
(2) Further, the first threshold value Th1 and the second threshold value Th2 are set based on the average value of 255 or 235 received light amount levels acquired immediately before. Therefore, an appropriate threshold value can be set according to the most recent light reception level state, and for example, it is possible to cope with a temporal change in the light reception level.

(3) Further, with respect to the second threshold Th2, an average value is calculated based on 235 received light signal data excluding 20 received light signal data captured immediately before the change from the non-detected state to the detected state. Configuration. This is because the most recent 20 received light signal data are acquired within the time T when the received light amount level changes greatly as shown in FIG. 3, and the average value including these must not be calculated.
(4) Further, in the detection state (FIG. 3C), since the comparison with the second threshold Th2 having a small margin is performed, the detection state is easily affected by, for example, noise. Therefore, the detection operation is performed under the condition that the comparison with the second threshold Th2 is invalidated until the predetermined time t1 elapses or the state where the received light amount level falls below the second threshold Th2 continues for the predetermined time t2.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.
(1) In the above embodiment, the fiber sensor is provided with the optical fibers F1 and F2. However, the present invention is not limited to this, and the light projecting head having the light projecting element 12 and the light receiving head having the light receiving element 13 are arranged to face each other. Ordinary transmissive photoelectric sensors may be used.

  (2) Further, although the glass wafer or the like is used as the object to be detected, the present invention is not limited to this, and the effect of the present invention can be obtained as long as it has optical transparency.

  (3) In the above embodiment, the received light amount level is read at each predetermined timing and each averaging process is performed. However, the present invention is not limited to this. For example, the received light amount level within a predetermined time is averaged by an integration circuit. Analog processing may be used.

  (4) Further, in the above embodiment, whether or not the process of invalidating the comparison with the second threshold Th2 and the state in which the received light amount level is lower than the second threshold Th2 continues for the predetermined time t2 until the predetermined time t1 elapses. However, the present invention is not limited to this, and any one of the processes may be selected and only one of the processes may be executed. Of course, a configuration in which neither of the two processes is executed may be used.

  (5) In the above-described embodiment, the configuration is such that the presence / absence of the wafer W is merely detected. However, the present invention is not limited to this. 2 may be configured to measure the dimension of the wafer W based on the time until the threshold value Th2 is exceeded (the duration of the detection state shown in FIG. 3), or detect whether the wafer W matches a predetermined reference dimension.

The perspective view which shows the use condition of the wafer detection apparatus which concerns on one Embodiment of this invention. Block diagram showing hardware configuration of wafer detector Explanatory diagram showing the relationship between wafer movement and received light level shift Flow chart showing control contents of control circuit

Explanation of symbols

10 ... Wafer detection device (photoelectric sensor)
12 ... Projection element (projection means)
13: Light receiving element (light receiving means)
16 ... Control circuit (determination means, threshold setting means, average value measurement means, invalidation means)
F1, F2 ... Optical fiber Th1 ... First threshold Th2 ... Second threshold T ... Time (predetermined period)
W: Wafer (object to be detected)
X: Detection area

Claims (6)

A light projecting means for emitting light to a predetermined detection region in which a detection object having light permeability moves;
A light receiving means arranged to receive light emitted from the light projecting means and transmitted through the detection region;
Threshold setting means for setting a threshold;
The received light amount level of the light receiving means that changes due to the presence of the detected object is compared with a threshold value set in the threshold setting means, and when the received light amount level is equal to or less than the threshold value, the detected object A detection unit that determines that the detected object is in a non-detected state when the threshold value is exceeded, and a photoelectric sensor comprising:
The threshold setting means, when the determination result of the determination means is in the non-detection state, the light reception amount level in the non-detection state and the light reception when the edge of the detection object is located in the detection region While setting a first threshold between the quantity levels,
On the condition that the determination result in the determination means has changed from the non-detection state to the detection state, the received light amount level in the non-detection state and the portion other than the edge of the detected portion in the detection region A photoelectric sensor characterized in that a second threshold value is set between the received light amount level when positioned. In the non-detection state, the light receiving amount level in the light receiving unit is read, and an average value measuring unit for obtaining an average value of a plurality of light receiving amount levels read within a predetermined period,
The photoelectric sensor according to claim 1, wherein the threshold setting unit sets the first and second thresholds based on an average value obtained by the average value measuring unit. 3. The photoelectric sensor according to claim 2, wherein, when the second threshold value is set, the predetermined period is a period before a certain period immediately before the change from the non-detection state to the detection state. The system further comprises invalidating means for invalidating the comparison operation with the second threshold value in the determination means for a predetermined period from the time when the received light amount level at the light receiving means falls below the first threshold value. The photoelectric sensor in any one of Claims 1-3. In the comparison operation with the second threshold value, the determination unit determines that the light receiving level at the light receiving unit is in the non-detection state on the condition that the state in which the light reception amount level exceeds the second threshold value has continued for a predetermined time. The photoelectric sensor according to any one of claims 1 to 4, wherein: A wafer detection apparatus for moving a predetermined detection region and detecting a dimension of a wafer as an object to be detected having optical transparency,
The photoelectric sensor according to any one of claims 1 to 5,
A wafer detection apparatus comprising: a dimension detection unit configured to detect a dimension of the wafer based on a continuation time determined as a detection state by the determination unit of the photoelectric sensor.

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