JPS63293449A - Drip detecting device for glass plate - Google Patents

Abstract

PURPOSE:To detect a drip distinctively from other defects by providing two photodetectors, an electric signal processing circuit, etc. CONSTITUTION:Photodetectors 12 and 13 photodetect transmitted light and reflected light when a laser spot makes a scan 11 on the defect of a transparent glass plate and photoelectron multiplier tubes 14 and 15 convert those light beams into electric signals. An electric signal processing circuit 16 processes the electric signals from the multiplier tubes 14 and 15 to generate defect data containing information on the kind and size of the defect. Further, an information processor 18 receives a defect pattern and position information from a defect data input circuit 17 and matches it with a defect discrimination pattern table 19 to discriminate the kind, size, etc., of the defect, thereby sending the discrimination result and position information to the an information processor. At this time, a drip sticking on the surface of the glass plate is larger in reflection factor than glass, so when the light spot strikes on the drip, the quantity of reflected light varies. The drip is accurately detected from a combination of detection results of the variation in the quantity of the reflected light.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a detection device for detecting drips, which is one of the drawbacks of glass plates.

[Conventional technology]

Defects that exist in glass plates include drips that are formed when tin from the bath in the manufacturing line adheres to the surface of the glass plate, and foreign substances that are formed when foreign objects such as bricks remain inside the glass plate. There are ridges formed when melted foreign matter remains inside the glass plate in the form of a trail, and bubbles formed when air bubbles remain inside the glass plate.

A defect detection device that detects such defects during the temporary glass manufacturing process feeds the detection results back to the transparent glass plate manufacturing process to prevent defects from occurring at the location where they occur and improve product yield. is needed.

The detection device used to detect defects on glass plates is a flying spot type that scans a light spot on the glass plate. This is done by detecting changes in the amount of light.

[Problem that the invention seeks to solve]

Drips are different from general foreign matter, and the size of drips increases, for example, in the so-called BTL processing process (processing of heating, bending, and pressurizing laminated glass for automobiles). For example, a drip of 0.2mm x O, 2III11 becomes 0.5mm
It becomes 1111. Therefore, it is necessary to detect drips of, for example, 0.2++us Xo, 2n+s or more at the stage of the glass plate manufacturing process.

However, with conventional drip detection devices that detect transmitted light,
If an attempt is made to detect a drip larger than 0.2 mm xo or 2 mm, all foreign objects larger than this size will be detected as defects, resulting in a problem of poor product yield.

An object of the present invention is to solve such problems and provide a defect detection device that can distinguish drips from other defects, that is, identify and detect that a defect is a drip.

[Structure of the invention]

The present invention provides a flying spot type drip detection device that detects drips adhering to the surface of the glass plate by scanning the entire surface of a glass plate running in the length direction with a light spot in the width direction. The presence of drip is determined from the combination of the first light receiving means that receives light, the second light receiving means that receives reflected light from the glass plate, and the change in the amount of light received by the first and second light receiving means. It is characterized by comprising a processing means for detecting.

[Effect]

The light reflectance of drips (tin) attached to the surface of the glass plate is greater than the reflectance of the glass, so when the optical scrubber hits the drips, the amount of reflected light changes.

The present invention detects changes in the amount of reflected light in addition to the conventional detection of changes in the amount of transmitted light, and uses a combination of these detection results to detect drips with high accuracy.

〔Example〕

Next, an embodiment of the drip detection device of the present invention will be described.

FIG. 1 is a block diagram schematically showing the overall configuration of a drip detection device according to an embodiment of the present invention. The drip detection device of this embodiment includes a scanner 11 that reflects a laser beam with a rotating polygonal mirror to scan a laser spot on a moving transparent glass plate, and a scanner 11 that scans a laser spot on a moving transparent glass plate by reflecting a laser beam on a rotating polygon mirror. Two light receivers 12.13 each receive transmitted light and reflected light, a photomultiplier tube 14.15 converts the light received by each light receiver into an electrical signal, and an electric signal from the photomultiplier tube is Electrical signal processing circuit 1 that processes and generates defect data including information on the type and size of the defect.
6, the defect data, signal processing clock, and line synchronization signal generated by this electrical signal processing circuit are taken in, and a defect pattern consisting of a bit array representing the type and size of the defect present on the glass plate is formed from the defect data. and a defect data acquisition circuit 17 that adds position information to this;
The defect pattern and position information are received from the defect data acquisition circuit 17, and the defect type is checked against the defect identification pattern table 19 held in advance to determine the type of defect.

It is comprised of an information processing device 18 that identifies the size, etc., and sends the identification result and position information to a higher-level information processing device.

In addition, for the following explanation, the detector 20 shall be comprised by the scanner 11, the light receiver 12.13, and the photomultiplier tube 14.15.

FIG. 2 is a perspective view of the detector 20, and FIG. 3 is a schematic configuration diagram of the detector viewed from a direction perpendicular to the direction of travel of the transparent glass plate. Identical elements are designated by the same numbers.

The scanner 11 includes a laser light source 21 that emits laser light;
It is provided with a rotating polygon mirror 24 that receives laser light 22 from a laser light source 21 and rotates at high speed around an axis 23 that is parallel to the direction in which the transparent glass plate 10 travels (hereinafter referred to as the Y-axis direction). Note that the laser light source 21 shown in FIG.
The location of is shown different from the actual location to avoid obscuring the drawing.

The scanner configured as described above uses a moving transparent glass plate l.
It is installed above O.

A laser beam 22 emitted from a laser light source 21 is incident on a rotating polygon mirror 24 that rotates at high speed, and the rotating polygon mirror 24 directs the laser beam 22 in a direction perpendicular to the Y-axis direction (hereinafter referred to as the X-axis direction). The image is swung and projected onto the moving transparent glass plate 10, and the glass plate is scanned in the X-axis direction. Rotating polygon mirror 24
The laser beam 22 repeatedly scans the transparent glass plate work 0 each time its reflective surface changes due to the rotation of the laser beam 22 . transparent glass plate 1
Since the laser beam 0 travels in the Y-axis direction, the entire surface of the glass plate is scanned by the laser beam.

Note that, as shown in FIG. 3, the laser beam 22 is
The light is projected onto the transparent glass plate 10 at an incident angle α in the Y-axis direction with respect to the normal line perpendicular to the glass plate surface. This is to prevent light reflected from the back surface of the transparent glass plate 10 and then reflected from the front surface from interfering with transmitted light. Note that it is desirable that the value of α be 13° or more.

Next, the arrangement and configuration of the two light receivers will be explained. One photoreceiver D1 for detecting the transmitted light 25 is arranged on the opposite side to the side where the scanner is provided, that is, below the transparent glass plate 10, and above the transparent glass plate 10 for detecting the reflected light 26. One light receiver D5 for detection is arranged.

These two receivers D1. D5 basically has the same structure and has a light receiving surface that is elongated in the X-axis direction. Hereinafter, the structure of the light receiver D'l will be described as a representative example.

FIG. 4 is a perspective view of the light receiver D1. This light receiver D1 is formed by arranging a large number of optical fibers 31,
One ends of the optical fibers 31 are arranged in two rows as shown in the figure and embedded and fixed in a resin or the like to form a light receiver body 32. The end faces 33 of 31 of the many arranged optical fibers come together to form an elongated linear light receiving surface 34. The other ends of the optical fibers are bundled and connected to a photomultiplier tube, which will be described later.

Note that in the above example, the optical fibers are arranged in two rows, but the arrangement method is not limited to this.

The light receiver D5 that detects the reflected light 26 may be constructed of an optical fiber as described above, but a scattering box is used and the light collected by the scattering box is sent to a photomultiplier tube, which will be described later, through the optical fiber. Something like this is fine. In this case, it is preferable to provide a mask having slits on the light receiving surface of the scattering box to block unnecessary light.

The detector 20 (FIG. 1) further includes two photomultiplier tubes PMI and PM5, as shown in FIG. is connected to the photomultiplier tube PM5, and the other end of the optical fiber of the photoreceiver D5 is connected to the photomultiplier tube PM5. Each photomultiplier tube converts the light received by each photoreceiver into an electrical signal.

Although not shown, an optical fiber for forming a start pulse is provided in the laser beam 22 reflected by the rotating polygon mirror 24 of the scanner, and a photoelectric fiber is provided to convert the light received by this optical fiber into an electrical signal. It is equipped with a converter and a pulse shaper to form a start pulse ST. This start pulse ST is used as a scanning start signal in a defect data acquisition circuit, which will be described later.

Now, the operation of the detector configured as described above will be described in the case where a drip exists on the transparent glass plate 10 and the laser beam scans this drip.

When a drip exists on a transparent glass plate, when this drip is irradiated with a laser beam, a change occurs in the amount of transmitted light and reflected light.

Changes in the amount of transmitted light are detected by a photodetector D1, and changes in the amount of reflected light are detected by a photoreceiver D5, which are sent to photomultiplier tubes PMI and PM5, respectively, and converted into electrical signals.

As described above, from the detector 20, changes in the amount of transmitted light and reflected light caused by defects in the transparent glass plate are sent as electrical signals to the electrical signal processing circuit 16 (FIG. 1).

Next, an electrical signal processing circuit 1 processes electrical signals sent from each photomultiplier tube PMI, PM5 of the detector to generate defect data including information on the type and size of the defect.
The configuration of No. 6 will be explained.

FIG. 5 shows an example of an electrical signal processing circuit. This electrical signal processing circuit includes each photomultiplier tube PMI.

A defect data generation unit CT1. that processes the electrical signals from PM5 and generates defect data. It is composed of CT5.

The defect data generation unit CTI includes an amplifier 411 that amplifies the electrical signal from the photomultiplier tube PM1, a negative differentiator 412 that differentiates the falling edge of the signal from the amplifier 411, and a level of the signal from the negative differentiator 412. It is comprised of a comparator 413 that compares two detection levels, and pulse shapers 414 and 415 that pulse-shape the two signals output from the comparator 413, respectively.

The defect data generation unit CT5 includes an amplifier 421 that amplifies the electrical signal from the photomultiplier tube PM5, a plus differentiator 422 that differentiates the rise of the signal from the amplifier 421,
It is comprised of a comparator 423 that compares the level of the signal from the plus differentiator 422 with two detection levels, and pulse shapers 424 and 425 that pulse-shape the two signals output from the comparator 423, respectively.

Next, the operation of this electrical signal processing circuit 16 will be explained with reference to the waveform diagrams of FIGS. 6 and 7.

First, the operation of the defect data generation unit CTI will be explained. The defect data generation unit CTI generates defect data including information on the type and size of the defect from an electric signal obtained by converting transmitted light detected by the light receiver D1 by the photomultiplier tube PMI.

The amplifier 411 amplifies the electrical signal sent from the photomultiplier tube PMI. Here, FIG. 6(a) shows the output voltage waveform of the amplifier 411 when the laser beam of the detector scans the transparent glass plate free of defects one time in the X-axis direction. From time 1. During one scan up to this point, transmitted light is received by the photoreceiver Di, which indicates that the output level is E volts. In this way, the receiver DI is 1
During the scanning period, transmitted light is constantly received.

If a transparent glass plate has defects, including drips, when a laser beam is projected onto the defects, the amount of transmitted light decreases, and a falling pulse appears in the output waveform as shown in Figure 6(b). 51 occurs. For convenience of explanation, this falling pulse 51 is shown in an exaggerated manner, and it is assumed that it falls at time t3 and rises at time t4. The magnitude of the falling level of this falling pulse 51 is proportional to the magnitude of the defect.

The negative differentiator 412 negatively differentiates the output from the amplifier 411, and as shown in FIG. 6(c), the falling time t of the falling pulse 51.

A differential pulse 52 that rises at . The magnitude of this differential pulse is proportional to the falling level of the falling pulse 51.

Differential pulse 52 from negative differentiator 412 is sent to comparator 4
13. The comparator 413 has two detection levels dll+adz as shown in the waveform of FIG. 6(e).
(d++<dtt), and these detection levels are compared with the falling level of the input differential pulse 52.

When the falling level of the input differential pulse is higher than the detection level d, the comparator 413 outputs the pulse from the first output terminal 416, and when it is higher than the detection level d1g, it outputs the pulse from the second output terminal. 417 outputs a repulse. These pulses are shaped by pulse shapers 414 and 415, respectively, and output as defect data DIllI)+g. In the case of the differential pulse 52 shown in FIG. 6(C), the falling level is thicker than the detection level dll (d is smaller than 2, so the defect data D1 as shown in FIG. 6(d)
1 is output. Defect data DII+ as above
DI! The other represents the size of the defect. In addition, the defect data DI+, I)+z indicates that the type of defect is drip,
Obtained for all cases of foreign bodies, stent, and bubbles.

Next, referring to the waveform diagram in FIG. 7, the defect data generation unit CT
The operation of step 5 will be explained. The defect data generation unit CT5 generates defect data including information on the size of drip from an electric signal obtained by converting the reflected light detected by the photoreceiver p5 by the photomultiplier tube PM5.

The light receiver D5 always receives reflected light from the surface of the glass plate, and the photomultiplier tube PM5 always sends an electric signal. FIG. 7(a) shows the waveform of the electrical signal from the amplifier 421 when the drip is scanned. Time t
, a rising pulse 61 is generated between time t6 and time t6. The positive differentiator 422 positively differentiates the output from the amplifier 421, and as shown in FIG. 7(b),
A differential pulse 62 that rises at the rising time t of the rising pulse 61 is output. The magnitude of this differential pulse is proportional to the rising level of the rising pulse 61.

The differential pulse 62 from the plus differentiator 422 is sent to the comparator 42
3 is input. The comparator 423 detects two detection levels d51. as shown in the waveform of FIG. 7(b). d%
1 (ds+<dsz), and these detection levels are compared with the rising level of the input differential pulse 62.

When the rising level of the input differential pulse 62 is higher than the detection level dsl, the comparator 423 outputs a pulse from the first output terminal 426, and the detection level dS! If it is higher, a repulse is output from the second output terminal 427. These pulses are shaped by pulse shapers 424 and 425, respectively, and output as defect data D and 1°DSL. In the case of the differential pulse 62 shown in FIG. 7(b), the rising level is thicker than the detection level dsl (d, smaller than 2), so the defect data D as shown in FIG. 7(c)
S+ is output. Defect data DSI as above
+D 52 indicates the size of the drip.

As explained above, the electrical signal processing circuit 16 outputs the defect data DI1 including information representing the type and size of the defect.
．． DI21 DSII Dsz is output and sent to the defect data acquisition circuit 17 (FIG. 1). In addition,
In the following description, it is assumed that defective data as a pulse corresponds to bit "1".

Next, the configuration of the defect data acquisition circuit 17 will be explained.

FIG. 8 shows an example of its configuration. This fault data acquisition circuit includes an X-axis counter 71, an OR unit 72, a frequency dividing circuit 73, a Y-axis counter 74, and a continuity determination section 75.
The continuity determination section 75 includes a defect data compression section 77, an X-axis continuity determination section 78, and a Y-axis continuity determination section 78.
and an axis continuity determination section 79.

The X-axis counter 71 uses a clock CL for X-coordinate division.
This is a counter that counts K, and is reset by a start pulse ST that is a scan start signal. This start pulse ST is applied to the rotating polygon mirror 2 of the detector 20 as described above.
4 is reflected by a glass fiber at a specific position, photoelectric conversion is performed, and waveform shaping is performed. The X-axis counter 71 outputs the counter value when the defect data is taken in to the continuity determination section 75 as X-coordinate position data.

The OR unit 72 is a unit that stores defect data for multiple scans from the electrical signal processing circuit and outputs it at a predetermined timing. Such an OR unit is described in Japanese Patent Publication No. 56-39419 "Defect Detection Device" ” is disclosed.

The frequency dividing circuit 73 divides the frequency of a line synchronization signal PC corresponding to the moving distance of the glass plate in the line direction, which is supplied from a pulse generator (not shown), and inputs the result to the OR unit 72 . The OR unit 72 outputs the accumulated defect data to the continuity determination section 75 at the timing of the frequency-divided line synchronization signal PG.

The Y-axis counter 74 counts the frequency-divided line synchronization signal PG from the frequency dividing circuit 73, and when defect data is input,
The count value is output to the continuity determination section 75 as X coordinate position data. Note that the Y-axis counter 74 is reset by software.

FIG. 9 shows an example of the OR unit 72. This OR unit 72 generates a plurality of types of defect data DIl.

Logical sum circuits OR++, OR+z, ORs+, 0Rsz corresponding to D1□, Ds+, and Dsz, respectively, and random access memories RAM++, RAM+z, and RAM5+
.

RAM, 2, and gate circuit a11. elf, c
It is composed of S,, Gst.

10 and 11 are diagrams to help understand the operation of the OR unit 72, and FIG. 10 shows the relationship between scanning by the laser spot, the clock CLK, and the line synchronization signal PC after frequency division. The schematic diagram, FIG. 11, is a diagram showing a state in which defect data D is stored in the RAM lr of the OR unit. The operation of storing the defect data D11 in the OR unit 72 as an example will be described with reference to these drawings. It is assumed that the glass plate is scanned n times in the X-axis direction by the laser spot during the frequency-divided line synchronization signal PC. In addition, each RA of the OR unit 72
It is assumed that M has addresses up to 1000. Each R
The AM address corresponds to the number of the clock CLK.

Now, when there is a drip 80 on the transparent glass plate 10 as shown in FIG. 10, the defect data DIl input from the electric signal processing circuit in the first scan is written to RAM r 1 and stored at addresses 502 and 503. bit “l”
The defect data DIS inputted in the second scan is ORed with the defect data read from RAM s in the OR circuit ORI+, and then
The defect data D11 rewritten to + and inputted in the n-th scan is ORed with the defect data read from the RAM I in the OR circuit, and then transferred to RAM II. The data is rewritten and finally bit "1" is stored in addresses 501 to 504. The defect data D stored in the RAM 11 in this way is the line synchronization signal PG whose frequency is divided by the frequency dividing circuit 73.
At the timing of , the continuity determination unit 75 passes through the gate circuit Ct+.
is output to.

The continuity determination section 75 compresses the defect data from the OR unit 72 and outputs the type of the compressed defect data, and the defect data compression section 77 determines the continuity of the compressed defect data in the X-axis direction. , an X-axis continuity determination unit 78 that outputs a start address and an end address in the X-axis direction, and an X-axis continuity determination unit 78 that determines the continuity of the compressed defect data in the Y-axis direction and outputs a start address and an end address in the Y-axis direction. It consists of a Y-axis continuity determination section 79.

Now, with reference to FIGS. 12 and 13, the operation of the continuous leg portion 75 having such a configuration will be explained. 12th
The figure is a diagram for conceptually explaining the operation of the defect data compression unit 77 that compresses ζ defect data, and FIG. 13 is a diagram for explaining the operation of the X-axis continuity determination unit 78 and the Y-axis continuity determination unit 79. FIG. 2 is a diagram showing an example of a bit arrangement of defect data after compression.

The OR unit 72 outputs defect data D for each type.
D, , , D, , , D, are output (However, as shown in Figure 12, the defect data for each type is a two-dimensional bit array in the X-axis address and Y-axis address directions. Now, considering a three-dimensional space, and assuming that these two-dimensional array defect data D++, D+□+DSl+D,! are arranged in the X-axis direction, the OR unit 72 outputs three-dimensional defect data. Data group D1.

It can be considered that Dot, Dss, and Dsx are output. The defect data compression unit 77 ORs all defect data in the X-axis direction for the three-dimensional defect data group all, D, t+ Ds+, Dsg corresponding to the X-axis address and the Y-axis address, and converts the three-dimensional defect data group all, D, t+ Ds+, Dsg into compressed two-dimensional Create a defect data DB. In FIG. 12, defect data D, l
An example is shown in which bit "l" is set only in defect data I)sz.

FIG. 13 shows an example of a bit array of defect data compressed based on the above idea.

The X-axis continuity determination section 78 and the Y-axis continuity determination section 79 check the continuity of bit "1" in the X-axis direction and the Y-axis direction, respectively, and detect a break in bit 61''. Determine whether to combine in the X-axis direction and Y-axis direction.

FIG. 13(a) shows a defect data block synthesized by continuity determination when both the varata of the X-axis continuity determination section 78 and the Y-axis continuity determination section 79 are 0.

The X-axis continuity determination unit 78 outputs address 500 as the X-axis start address and address 503 as the X-axis end address of this defective data block.

On the other hand, the Y-axis continuity determination unit 79 outputs address 100 as the Y-axis start address of the defective data block and address 103 as the Y-axis end address.

FIG. 13(b) shows a defect data block synthesized by continuity determination when the parameters of the X-axis continuity determination section 78 and the Y-axis continuity determination section 79 are both 1.

If the parameter is 1, the bit"
Even if there is a 1" discontinuity, they are combined and a defective data block as shown is synthesized. In this case, the X-axis continuity determination unit 78
From here, address 500 is the X-axis start address of this defective data block, and address 50 is the X-axis end address.
Address 3 is output.

On the other hand, the Y-axis continuity determination unit 79 outputs address 101 as the Y-axis start address and address 103 as the Y-axis end address of the defective data block.

By performing continuous judgment that interpolates and combines the discontinuous bits of "1" in this way, when a single defect is scanned by a laser spot, the timing of generation of defect data from multiple receivers is shifted. In such a case, use these as 1
This makes it possible to recognize that the data is defect data from individual defects.

The Y-axis continuity determination unit 79 determines whether the bit "1" standing in the defective data block is determined when the continuity of the bit "1" is interrupted.
1'', that is, the type of defect data is a defect pattern, and the X-axis continuity determination unit 78 and Y-axis continuity determination unit 79 determine the start address, end address, and start address, end address in the X-axis direction, and the start address, end address in the Y-axis direction of the defect data block. FIFO memory 76 with address as defect position information
Output to. Note that the Y-axis continuity determination unit 79 has a bit “
1'' in the Y-axis direction is forcibly cut for a predetermined length, and the defect pattern and position information are output to the FIFO memory 76.

The FIFO memory 76 stores the sent defect pattern and position information, and transfers it to the memory of the information processing device 18 by direct memory access.

The information processing device 18 holds in advance a defect identification pattern 19 for determining the type of defect and the size of the defect.
The defect pattern sent from the defect data acquisition circuit 17 is compared to identify the type and size of the defect. If the defect is a drip, in addition to the defect data D11 or I)tz, the defect data D! Since i++[)sz always exists in the defect pattern, the information processing device can recognize that the defect is a drip by comparing it with the defect identification pattern table. Further, the size of the drip is identified depending on which defect data exists in the defect pattern. The information processing device 18 further identifies the location of the defect from the location information sent from the defect data acquisition circuit 17, and sends these identification results to the higher-level information processing device.

The upper level information processing device controls the manufacturing line process, plate sampling process, etc. based on the sent information.

Although the identification type defect detection device for transparent plate glass has been described above, the present invention is not limited to this embodiment, and it goes without saying that various modifications and changes can be made within the scope of the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, drips adhering to the surface of a glass plate can be removed from other defects such as foreign matter, stylus, etc.
Since it is possible to identify and detect bubbles and further detect their size, it becomes possible to effectively detect small drips.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of an embodiment of the drip detection device of the present invention; FIG. 2 is a perspective view of the detector; FIG. 3 is a side view of the detector; Figure 5 is a block diagram of the electrical signal processing circuit; Figures 6 and 7 are waveform diagrams for explaining the operation of the electrical signal processing circuit; Figure 8 is defect data acquisition. A block diagram of the circuit, FIG. 9 is a circuit diagram of the OR unit, FIGS. 10 and 11 are diagrams for explaining the operation of the OR unit, and FIGS. 12 and 13 are the operations of the continuity determination section. FIG. 10... Transparent glass plate 11... Scanners 12, 13... Light receivers 14, 15... Photomultiplier tube 16... Electric signal processing circuit 17... - Defect data acquisition circuit 18... Information processing device 19 -... Defect identification pattern table 20...
・Detector 21... Laser light source 24... Rotating polygon mirror 71... X-axis counter 72... OR unit 73... Frequency dividing circuit 74... ... Y-axis counter 75 ... Continuity judgment section 76 ... FIFO memory 77 ... Defect data compression section 78 ... X-axis continuous format foot section 79 ...・Y-Axis Continuous Judgment Attorney Patent Attorney Yoshikazu Iwasa ==--==-===--J Figure 2 Figure 3 To the bottom Figure 4 t, t22O2 Figure 7 Figure 9 Figure 10 Y Figure 12

Claims (1)

[Claims] (1) In a flying spot type drip detection device that scans the entire surface of a glass plate traveling in the length direction in the width direction with a light spot and detects drips adhering to the surface of the glass plate, the transmitted light from the glass plate is received. A second light receiving means receives reflected light from the glass plate, and the presence of drip is determined from the combination of changes in the amount of light received by the first and second light receiving means. A drip detection device for a glass plate, comprising a processing means for detecting drip.