GB2071641A - Apparatus for Detecting Defects in Glass Containers - Google Patents

Abstract

The apparatus is especially designed to detect "birdswing" defects and comprises a linescan photodiode array camera (6) which views light refracted from a rotating container under inspection (2), the light being produced by a source of illumination (4). The photodiode array is linear and disposed parallel to the longitudinal axis of the container. Any defects such as birdswings will show as dark areas on a normally light background. Electronic circuitry is provided enabling the user to preset the number of camera scans and the length of the diode array over which the dark area exists before a defect present signal is produced. This provides a control to the minimum dark area which must exist on the container before a defect is signalled and prevents minor blemishes from triggering such a signal. <IMAGE>

Description

SPECIFICATION Apparatus for Detecting Defects in Glass Containers This invention relates to apparatus for detecting defects in glass containers, and particularly to apparatus for detecting defects known as "bird swings" which sometimes occur in glass containers produced in automatic high speed glass container moulding machines.

A bird swing defect in a moulded glass container is essentially a thread of glass within the container and extending between two positions on the inner wall of the container. The two positions are generally at the same height and diametrically opposed, and the thread of glass extends across the inside of the container to give the appearance of a swing or perch for a bird-hence the name of this form of defect.

Bird swing detectors which optically sense for such faults are known. In one particular commerciai detector, the glass containers to be inspected are passed along a conveyor, are side illuminated and shadows appearing on the container are optically detected as faults of the bird swing type. In order to detect shadows of all positions on the container sides, three optical detectors are employed. Initially two are disposed at approximately 450 and 135 to the line of movement of the container, the container is then partially rotated (through about 1 800) and the third detector then views the container side at approximately 900 to the line of movement. The optical detectors are focussed on the side surface of the container remote from the detectors and rely on se,nsing the presence of shadows thereat.

Apart from their complexity, current bird swing detectors suffer from the disadvantage of not easily being able to discriminate between true defects and marking such as lettering purposely moulded into the side wall of the container.

We have now devised an improved bird swing detector which employs only one optical detector and which is capable of discriminating between moulded lettering and bird swing defects.

According to the present invention there is provided an apparatus for detecting defects in a glass container, which comprises means for illuminating the side wall of a container under inspection, means for sensing the intensity of light refracted from the side wall in a direction parallel to the longitudinal axis of the bottle, means for providing relative rotation through substantially 3600 about said longitudinal axis between said container and said sensing means, and means responsive to said sensing means for signalling that a defect is present when a light intensity below a preset level is present for a p.adetermined length of time during said rotation and for a predetermined distance along said longitudinal axis.

Preferred features of the invention will now be described with reference to the accompanying drawings, given by way of example, wherein: Figures 1 and 2, are schematic end and plan views of a bird swing detector in accordance with the invention, and Figure 3 is a schematic electrical circuit diagram of the detector illustrated in Figures 1 and 2.

Referring to Figures 1 and 2 the detecting station of a bird swing detector according to the invention is shown with a container 2 having such a defect passing therethrough. The container is illuminated from the side with white light from a light boss 4, and diametrically opposed to the latter is situated a linescan photodiode array camera 6 (obtainable from Integrated Photomatrix Ltd, Dorchester, Dorset) which is slightly below the transverse axis of the container and which views at an oblique angle the near side wall of the container at 8. The camera 6 output is supplied to electronic processing circuitry 10 described below. Each container passes through the detecting station on a conveyor 12 and is rotated 3600 by contrarotating belts (not shown) whilst within the viewpoint of camera 6.The single camera 6 thus sees the complete, rotated side wall of each container passing through the detecting station.

A pair of photodiodes 14 are disposed at container neck height and act as gauging markers so that the camera 6 and circuitry 10 only actively sense for defects when the neck of any container is between the two photodiodes 14. This arrangement avoids difficulties with the side edges of the containers or the axial seam of the container produced during moulding being sensed as a defect as any container just enters or leaves the detecting station.

The camera 6 includes a linear array of 128 photodiodes which are sequentially scanned at high speed. The camera provides a number of output signals: start scan pulse signal SS (a pulse being supplied each time a scan of the 128 photodiodes commences), a clock pulse signal CK (synchronous with the scanning of each photodiode) and a video output signal. The video output signal is an analog signal representative of the light intensity received by the scanned (sequentially interrogated) photodiodes. This analog signal is converted to digital form by comparing it to a preset level in a level detector, so providing "on" signals above the level and "off" signals below the level. These on/off signals are termed herein squared video signals, AV.In the absence of defects in the containers, the latter refract the light from light box 4 so that the photodiode array (which is disposed parallel to the longitudinal axis of the containers-i.e.

vertical) receives such refracted light. The level detector is set to provide "on" AV signals in such light. In the presence of a bird swing defect, or even markings purposely moulded into the container side wall, at least some of the photodiodes will see a shadow: the level detector providing an "off" AV signal.

In processing the camera outputs to detect bird swing defects accurately, a number of parameters are preset in the circuitry 10.

It is possible that not all of the 128 linear photodiodes in camera 6 are required to sense light refracted from the container side wall. This is especially so since the apparatus may be employed to sense defects in containers of different heights. Thus, if the linear array of photodiodes are numbered from 1 at the bottom to 128 at the top (see Figure 1), for example only the outputs of diodes number 20 to 100 need be processed to detect bird swing defects. A first parameter which is chosen in circuitry 10 is therefore the uppermost and lowermost out of the 128 possible diodes which are to be employed.

A second parameter which is preset is the number of adjacent (i.e. consecutive) photodiodes in the array which in any one scan must sense a shadow (AV low) to satisfy the criterion that it is a true bird swing defect. For example, a minor blemish on the container side wall may cause a shadow on, say, one or two adjacent photodiodes in any one scan which one would not wish to term defect. Thus, one selects the minimum number of photodiodes which must view a shadow in any one scan before actuating a "defect present" signal. This parameter essentially sets the distance along the longitudinal axis of the bottle for which the shadow must be present to actuate the "defect present" signal.

A third preset parameter is the number of consecutive scans of the photodiode array for which a shadow on the preset number of photodiodes exists. This parameter is to enable the apparatus to discriminate true bird swing defects from purposely-moulded markings such as letters. Since the containers are rotated by 360 at the detecting station, any one moulded letter would only present a shadow during a small number of scans. A bird swing defect, on the other hand, would show as a shadow for a much larger number of scans, and possibly nearly all the scans as the bottle rotates 3600 between the two gauging photodiodes 14. This parameter essentially sets the minimum time for which the shadow must be present before being decoded as a true bird swing defect.

The electronic circuitry employed to process the outputs of the camera 6 is illustrated in Figure 3, where only the more important components are illustrated for clarity. A pair of thumbwheel stores 20 are present with the sequence number of the lowermost and uppermost diodes in the array of 128 which are to be employed for defect detection. This is the first parameter described above and, in the example given, setting numbers 20 and 100 in the thumbwheel stores will ensure that diodes only from 20 to 100 are employed for defect detection.

A continuous series of "1 "s are clocked by the CK signal from camera 6 through a shift register 22 and the latter is cleared by the SS signal from camera 6. The states of the shift register stages are compared to the numbers held by thumbwheel stores 20, and a pulse output is provided at 24 which commences at the lowermost diode number preset (20 in our example) and terminates at the uppermost number preset (100 in our example).

The pulse from 24 is supplied to an AND gate 26, a second input of which receives a AVsignal from camera 6. AND Gate 26 is connected to a second AND gate 28 which has AV and CK inputs of two other terminals. The output of AND gate 28 is employed to clock a shift register 30 which has a continuous series of "1 "s clocked therethrough. Shift register 30 is cleared by SS signals from camera 6 and the output stages are each compared to a preset number held in a thumbwheel store 32. This latter store is present with the second diodes which must be in shadow in any one scan before a "defect present" signal is actuated. The comparison output is stored in a flip-flop 34, which is in the "1" state if the preset number of diodes in shadow in any one scan is achieved, but which is otherwise in the "0" state.

A further shift register 36 has a continuous series of "1 "s clocked through by the SS signals from camera 6 and is cleared by the Q output of flip-flop 34. The output stages of shift register 36 are compared to a number preset in a thumbwheel store 38. This latter store is preset with the third parameter described above the number of consecutive scans for which a "defect present" signal must exist before it is considered to be a true defect (as opposed to purposelymoulded marking). When a "defect present" signal is set by flip-flop 34 (Q=O), shift register 36 advances a "1" for each scan and if this occurs for a sufficient number of scans corresponding to the number preset in thumbwheel store 38 then an output signal is supplied to a gate 40. If the "defect present" signal is not present for the predetermined number of scans then the Q output of flip-flop 34 goes high to clear shift register 36.

Gate 40 is enabled/disabled by the gauging photodiodes 14 which act as an interrupt so that the circuit only signals that a defect is present when a container is within the gauging limits set.

The output of gate 40 is supplied to a visual display 42 for indicating to a machine operator that a defect has been detected. It is also supplied to a delay 44. When the latter is actuated then, after a preset delay, it actuates a container rejecting apparatus 46 which acts to remove the defective container from conveyor 12 after it has left the detecting station.

Claims (8)

Claims

1. An apparatus for detecting defects in a glass container, which comprises means for illuminating the side wall of a container under inspection, means for sensing, in a direction parallel to the longitudinal axis of the container, the intensity of light refracted from the side wall of the container, means for providing relative rotation through substantially 3600 about said longitudinal axis between said container and said sensing means, and means responsive to said sensing means for signalling that a defect is present when light intensity below a preset level is present for a predetermined length of time during said rotation and for a predetermined distance along said longitudinal axis.

2. An apparatus according to claim 1 wherein the sensing means comprises an opticallysensitive electronic sensor of elongate configuration disposed parallel in one plane to the longitudinal axis of the container under inspection.

3. An apparatus according to claim 2 wherein the sensor is disposed obliquely to said longitudinal axis in a plane orthogonal to the plane in which the sensor is parallel to said longitudinal axis.

4. An apparatus according to claim 2 or 3 wherein the sensor is a photodiode array.

5. An apparatus according to claim 2,3 or 4 wherein the sensing means includes means for successively scanning the output of the electronic sensor along its length so as to provide a repetitive video output signal representative of the intensity of light falling upon the sensor at positions along its length.

6. An apparatus according to claim 5 wherein said signalling means includes means for presetting the number of successive scans and for presetting the number of successive positions along the sensor length over which the light intensity must be below the present level before a signal indicative that a defect is present is produced.

7. An apparatus according to any of claims 1 to 6 which additionally include gauging means for detecting glass containers entering and leaving an inspection station of the apparatus, said apparatus only actively sensing for defects when the gauging means senses that a container is fully-disposed at the station.

8. An apparatus for detecting defects in a glass container substantially as herein described with reference to the accompanying drawings.