WO1992020994A1

WO1992020994A1 - Gob weight and dimension sensor

Info

Publication number: WO1992020994A1
Application number: PCT/GB1992/000936
Authority: WO
Inventors: Lars Tore Anderson
Original assignee: Bh-F (Engineering) Limited
Priority date: 1991-05-22
Filing date: 1992-05-22
Publication date: 1992-11-26
Also published as: GB9111066D0

Abstract

Data concerning the volume and/or weight of a glass gob (6) as it drops after being sheared off (by 7) is collected by imaging the gob on to an array of light-sensitive elements such as a CCD array in a camera (10) and electronically freezing the image and calculating gob volume/weight from the image via a microprocessor. Two images viewed at right angles (cameras 10, 15) give improved results. The data derived can be fed back, e.g. via a gob weight controller (13) to control the operation of forehearth equipment (1, 2, 3, 4, 5).

Description

GOB WEIGHT AND DIMENSION SENSOR.

This invention relates to gob weight and dimension sensing.

In the mass production of glass articles, extremely tight tolerances need to be placed on the weight of the pieces of molten glass successively fed to a glass forming machine. Conventionally, glass from a glass making furnace is fed along an extension to that furnace known as a forehearth and then through a basin from the base of which the glass is ejected as a succession of so-called gobs. The dispensing of each gob is effected by means of a vertically reciprocated plunger above an orifice in the floor of the basin and a cooperating pair of shears located immediately below the orifice which chop the emerging piece of glass allowing the gob to fall freely under the influence of gravity into a reception chute leading to the processing machine which turns the gob into the finished glass article. Such an arrangement may be twinned, i.e. two plungers, two orifices and two sets of shears. Flow control means located in the basin, and means for adjusting the stroke of the plunger may both be adjusted to produce a gob of the desired size. Continuous monitoring of the actual gobs produced is desirable in order to enable adjustments to take place during the operation and it is desirable to monitor gob size immediately after gob production since weighing the glass articles produced detects deviations from the desired gob weight only after an undesirably long time.

United States Patent Specification 4978859 discloses a method and apparatus for determining the size (and thereby the weight) of a freely falling gob of molten glass. The apparatus includes a one-dimensional photodiode array which "looks at" the gob as it falls and notionally divides the gob up into a large number of horizontal slices, the individual volumes of which are calculated and summed to provide the total gob volume or weight. Because the gob is falling freely under the effect of gravity, it is moving gradually faster as the trailing end of the gob passes the apparatus which means that the slices near the trailing end of the gob are thicker than those at the leading end. This requires additional mathematical processing to take this into account. Additionally, since the apparatus must "look at" the gob in free fall, the viewing window must be located at least the length of the gob below the shears, and at least the length of the gob above a gob reception chute. Installation is sometimes difficult or indeed impossible in glass making plants where insufficient physical space is available, or even if possible limits its use to relatively short gobs.

According to the present invention, there is provided a method of monitoring gob dimensions, weight and shape which comprises imaging the gob or gobs as they fall on to a two-dimensional array of light sensitive elements. detecting the condition of the light sensitive elements over a period of time sufficiently short effectively to freeze the image of the gob(s) thereon, deriving from such sensing geometrical data concerning the size and shape of the gob(s) and processing such data to provide an indication of the volume or weight of the gob(s) .

Preferably the two-dimensional array of light sensitive elements is an array of charge coupled devices, a so- called CCD array, each device being of very small areal extent, thus providing an automatically digitised image.

As disclosed in the United States specification referred to above, even greater accuracy may be obtained by providing two such arrays (per gob, if more than one) , each "looking at" the gob(s) at right angles to the other so that if the gob shape is not perfectly circular in horizontal section, but rather elliptical, this can be taken into account.

Preferably the apparatus includes means enabling the image of the gob(s) to be focussed on the array at variable magnification so that the image of the entire gob is, or gobs are, spread over most of the array. A conventional zoom lens system between the gob and the array may be used. An anamorphic lens system can be used optically to spread out the image on the two-dimensional array, thus improving accuracy. This feature is very desirable to enable good results to be obtained over a wide range of gob sizes, e.g. from 20 to 400 mm in length and 12 to 100 mm in width.

Preferably also the electronics associated with sensing the array is arranged to sense when elements in the array spaced slightly away from the edge of the array are first illuminated, such detection being then used as a trigger signal to trigger the full sensing of the whole array in order to derive the necessary data to enable gob size to be calculated.

CCD array television cameras are available in commerce and may be used in practising the present invention. For example, a CCD array television camera manufactured by Siemens AG under the designation K235 may be employed. Alternative suitable cameras are available from Sony Corporation and from Matsushita Electric Industrial Co Ltd under the trademark Panasonic. The main requirements for use in the present invention are high light sensitivity, predictable response, and an ability to operate under harsh conditions. In particular, the sensitivity should be such as to enable easy discrimination between light reflected from the gob and light reflected from water droplets which may be in its field of view and which arise from watercooling associated with the shearblade mechanism. Generally the camera should be able to operate at intensities of less than 1 lux, preferably much less, and be sufficiently sensitive to capture a complete image very fast, preferably in less than a millisecond. The image may be viewed essentially monochromatically, preferably in the red end of the visible spectrum.

Control of the camera and processing of the signal derived from the CCD array may be effected using a conventional microprocessor operated at sufficiently high speed to give effectively instant data on gob size or weight. Such a microprocessor may be adapted to emit control signals to appropriate gob weight control apparatus which may operate adjustments to the flow control means in the basin and/or the vertically reciprocating plunger. The program used for evaluation and camera control is preferably one which can evaluate not only whether a particular element of the CCD array in within or outside the image of the gob thereon, but in the case of elements of the array which are on the edge of the image evaluate the amount of illumination on a suitable gray scale, which considerably improves the accuracy of calculating the gob size and weight. If two cameras are under simultaneous microprocessor control, the signals can also be processed in real time to indicate any deviation of the main longitudinal axis of the gob from the vertical as it falls through the field of view of the camera, and any such deviation can be fed back into the calculations of gob size and weight to provide a more correct measurement.

A typical arrangement of the apparatus for a single orifice unit is shown diagrammatically in the accompanying drawing by way of example. In this, only the relevant parts of the apparatus are shown for clarity. The details of the forehearth structure are omitted.

Located in the pouring basin are the lower end of a rotatable cylinder 1 and a plunger rod 2.

Rotatable cylinder 1 can be moved up and down vertically via a shaft and cantilever arrangement 3 under the control of a motor 4. Plunger rod 2 is located at one end of an arm 5 which is vertically reciprocated by means not shown in order to dispense successive gobs 6 from an orifice at the base of the pouring basin. The vertical distance between the base of the inside of the pouring basin and the bottom of rotatable cylinder 1 determines in part the size of gob 6. The motion of the plunger will also affect the weight and shape of the gob. As the plunger rod 2 descends, it pushes molten glass through the orifice at the base of the pouring basin. The actual gob is formed by means of a pair of shears 7 which cut the gob from the glass pushed through the orifice.

As shown in the Figure, gob 6 passes through the field of view of a camera 10. The lens of the camera images the gob 6 on to a CCD array. At an appropriate point (determined by the programming of a microprocessor 11) the entire image (which, at this point, is on the CCD array) is captured and processed. If desired, the image of the gob may also be captured by a second camera 15, having a direction of view level with but at right angles to that of camera 10. Both cameras are installed in suitable water-cooled, air-purged housings to keep them operating stably and protect them from the advers environment below the forehearth. Data from both cameras can be compared to determine any ellipticity of crosssection and any tipping from the vertical as the gob falls.

By suitable programming of microprocessor 11, the weight of the gob may be calculated and displayed on a screen. The weight of the gob may also be compared with a desired gob weight and if desired a signal sent via a line 12 to a gob weight controller 13 which via a line 14 may control the motor 4 to raise or lower rotating cylinder 1, or emit a suitable control signal to movement control systems. If desired, an electronic scale 20 may be connected via a lead 21 to the microprocessor 11. This assists calibration and setting up of the unit.

The camera 10 may be located at any convenient point where it can see the gob 6 after it has been formed by shears 7 and before it drops into the subsequent machinery for forming the gob into the desired article, for example a glass container, a piece of moulded glassware or a moulded glass item such as a television tube or lamp housing. The space required for this is just greater than the length of the gob, thus enabling the method and apparatus of the present invention to be used in situations where there is a very short distance between the shears and the subsequent inlet chute of the processing machinery.

Claims

1. A method of monitoring the dimensions of gobs of fused glass falling seriatim from cyclically- operated shears, comprising the steps of producing an image of each gob in free-fall on to at least one two-dimensional array of light-sensitive elements; determining the condition of the light-sensitive elements over a period sufficiently short effectively to freeze the image of the gob thereon; deriving from the condition of the elements over that period data concerning the shape and size of the gob being monitored, and processing such data to provide an indication of the volume or mass of the gob.

2. A method as claimed in Claim 1, including the step of throwing two orthogonal images of each gob on to one each of two two-dimensional arrays to allow for the transverse cross-sectional shape of not truly circular gobs and to allow for variation in gob attitude.

3. Apparatus for monitoring the dimensions of gobs of fused glass falling seriatim from cyclically- operated shears, comprising means for projecting an image of each gob in free-fall on to at least one two-dimensional array of light-sensitive elements; means for determining the status of the elements over a period short enough to freeze the image of the gob thereon; means for deriving from the status information over that period data concerning the shape and size of the gob being monitored, and means for processing such data to provide an indication of the volume or mass of the gob.

4. Apparatus as claimed in Claim 3, including two two- dimensional arrays of light-sensitive elements; means for projecting on to each array one each of two orthogonal images, and means for operating on the sets of data from both arrays to allow for the transverse cross-sectional shape of the gob being not truly circular or for variation in gob attitude.

5. Apparatus as claimed in Claim 3 or 4, in which the or each array is of charge-coupled devices each of very small areal extent.

6. Apparatus as claimed in Claim 5, in which the or each array is integral with a camera focussed on the path of the gobs below a set of gob-forming shears.

7. Apparatus as claimed in any of Claims 3 to 6, including means for enabling the size of the or each image projected on to the array to be adjustable.

8. Apparatus as claimed in Claim 7, in which the adjustable size is provided by a zoom lens system located optically between the gob and the or each array.

9. Apparatus as claimed in Claim 8, in which the zoom lens system is anamorphic.

10. Apparatus as claimed in any of Claims 3 to 9, in which means are provided for triggering the derivation of status information over the whole of the or at least one array when an element spaced slightly inwardly from an edge of the array is first illuminated.

11. Apparatus as claimed in any of Claims 3 to 9, in which means are provided for triggering the derivation of status information over the whole of the or at least one array which operate in synchrony with the cyclically operated shears.

12. Apparatus as claimed in any of Claims 3 to 11, in which the data-processing means is used to control the gob-forming part of associated glass-making equipment to reduce any error between the desired and actual volume or weight of the gobs.

13. Apparatus as claimed in Claims 3 to 12, including a scale on which a gob can be weighed, to assist in the initial calibration of the apparatus.

14. Apparatus as claimed in Claim 13, in which the scale is electronic and arranged to feed weight data into the data-processor.