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The present invention relates to apparatus for examining the shape or dimensions of objects.
In the food canning industry empty cans are loaded on to a conveyor which transports them to a filling system.
If a can is deformed, it may jam in the filling system and/or cause damage to the latter. Thus, in the case of nominally round cans, it is desirable to check that cans with an ovality deformation do not pass to the filling system.
Another common fault present in cans is dinting, i.e. a deformation of the can lip. Excessive dinting can also create problems if the can passes to the filling system, in particular because the can may then not seal correctly.
While the present invention is especially suited to the pre-examination of cans, especially round cans used in food canning, it is not limited thereto, and may find application in the final testing of filled and sealed cans, e.g. for dents, and in testing other objects altogether such as bottled and shaped packages.
According to the present invention there is provided an apparatus for examining objects, said apparatus comprising:
a test station adapted for location on the path of a means for conveying the objects in a direction through said test station;
a means providing signals indicative of the speed of the conveying means;
electronic camera means at the test station for scanning a face of each object presented thereto, at least in a direction transverse to the conveying direction, said camera ~Z93Q5~
means providing output signals;
means for processing the camera output signals and said conveyor means speed signals to provide measurement signals indicative of a geometric property for each object scanned;
and comparator means for comparing the measurement signals with reference data signals and determining therefrom whether each object complies with preset measurement signal limits.
According to the present invention there is also provided an apparatus for examining objects each having an elliptical cross sectional face extending in a plane and bounded by a perimeter rim, said apparatus comprising:
a test station adapted for location on the path of a means for conveying the objects in a direction through said test station;
a means providing signals indicative of the conveying means speed of object conveyance;
a means for illuminating said object face with electro-zo magnetic radiation;electronic camera means at the test station for generating a plurality of electromagnetic scans of said object face presented thereto at least in a direction transverse to the conveying direction of the object, said camera means providing output signals associated with said electro-masnetic scans;
means for processing the camera output signals including.
a means for detecting signals corresponding to leading and trailing edges of object rim first and second sections displaced from one another in a direction approximately parallel to said conveying direction;
a means for detecting signals corresponding to leading and trailing edges of object rim third and fourth sections displaced from one another in a direction approximately lZ~3~ ri:~L
perpendicular to said conveying direction;
a computation means receiving s a id scanned object rim signals for computing magnitudes of displacement between selected ones of said leading and trailing object rim section signals in accordance with said conveyor means speed signals, and computing from said displacement magnitudes signals indicative of the magnitude of ellipticity of said object face; and Comparator means for comparing the computed object face ellipticity signals with reference data signals indicative of a preferred magnitude thereof and determining therefrom whether each object complies with preset limits.
Preferably, the camera means further scans in the direction of conveyor movement to provide said conveyor means speed signals.
The camera means may comprise a single camera scanning in two perpendicular directions, or it may comprise linear first and second cameras respectively scanning in two perpendicular directions, the first camera being capable or providing synchronization signals for the second camera.
Preferably, the computation means further comprises a means for determining a value of rim width from one of the object rim sections leading and trailing edge signals, the comparator means further comprising a means for comparing the measured value of rim width with reference data signals therefor and determining therefrom whether the object complies with preset limits for the object rim width.
The computation means may further comprise a means for determining values of rim width from associated leading and trailing signal portions of object rim first and second lZ93~)51 sections measured during a single scan and comparing the measured rim width values with one another determining therefrom whether the object complies with preset limits for said object rim width.
The computation means may further comprises a means for integrating signal magnitudes corresponding to a plurality of adjacent measured object rim widths obtained during - successive scans of said object.
Preferably, the apparatus includes means on the conveyor for turning the object through an angle, the camera means comprising a camera which scans the object in the same scanning direction both before and after it has been turned.
The conveying means may act intermittently to step a succession of spaced objects forward to the test station.
Preferably, the camera means comprises at least one charge-coupled camera device, the comparator means furthercomprises an alarm device, a conveyor stop device and an object reject mechanism, or the comparator means may further comprises a microprocessor, and the apparatus may further comprise a microprocessor for processing signals received from the camera means via an analog to digital converter.
It is within the scope of the present invention to develop the measurement signals within the computer, whcih in this instance would receive a digitised video signal output by feeding the output signals from the camera means through an analogue-to digital converter.
The invention will'now be exemplifiied with reference to the `" 12~3~S~
accompanying drawings, in which:
Figure 1 diagrammatically illustrates an object-testing apparatus in accordance with the invention;
Figure 2 is a block circuit diagram, and Figure 3 comprises a set of signal waveforms.
Referring to Figure 1, the apparatus of the invention includes a support 10 carrying an enclosure 12 and adapted to straddle a conveyor 14 on which cans 16 are being conveyed, e.g. empty cans in transport to a filling and sealing system.
On the enclosure 12 are mounted two linear CCD cameras 18, 20, together with a light source 22 which may be a diffused multiple tungsten lamp, fluorescent lamp or laser source such as a helium-neon laser providing a plane of lZ93~1 light through a cylindrical lens. The cameras 1~, 20 are supported vertically above the path of the moving cans to be tested, which path passes through the enclosure 12, so as to view the upper nominally round face 24 thereof which 5 is illuminated by the light source 22. One camera is aligned with its can direction on and along the locus of movement of the centre of the face 24; the other camera is aligned at right angles thereto, taking successive measurements normal to the direction of motion as the can lO passes underneath.
Also shown in the drawing are an electronic control box 26 housing primary logic circuitry and microcomputer, with access via an electronics control panel 28. The enclosure 12 also has a removable inspection panel 30 to enable cans 15 passing through the test station to be visually inspected, and also to enable insertion of test pieces for alignment and calibration purposes.
The first camera 18 provides, for example, a measurement of the maximum width (diameter) of the can from edge to 20 edge, and of the width of the edge rim at both the leading and trailing edges. In addition, the relative motion of the can as detected by this first camera is used to provide scan synchronisation for the second camera 20.
The electronic control circuitry 26, later described, 25 includes a timing clock to control camera operation and data processing, if desired accompanied by data read-out to a data logger. A line scan synchronising signal is provided to indicate the start of a new line.
The camera video signals are digitised with respect to the 30 set level of a discriminator, and the digitsed signals are .
`` 1293~1 processed and the measurement signals analysed by the computer.
In order to ensure reliability and repeatability of the measurements, the source 22 is driven by a d.c. power 5 supply (not shown) in order to achieve a constant and uniform illumination of the face of the can viewed by the cameras.
Downstream of the test station, an ejector mechanism (not shown) is controlled by a signal derived from the computer 10 to reject cans not meeting set standards of shape and dimension which are pre-set in or programmed into the computer.
Referring now to Figure 2, the control electronics include a clock 31 providing for generation of control signals 15 within the CCD camera 20, which scans perpendicular to the line of the conveyor. Generally analogous circuitry associated with the same microcomputer 32 may exist for the camera 18. The interface between the camera 20 and the computer 32 comprises, in addition to the clock 30, 20 integrated circuit logic which will now be described.
A start-new-line signal (SNL) is generated either by an external control (e.g. another camera such as camera 18) or by the computer or again the camera may be free-running as a sub-multiple of the scan clock. The SNL generator 40 25 (or the control signals generator in the camera) set the new-line-detected latch (NLD) 42. The video signal from the camera 18 is converted to a digital signal in the discriminator (disc) 44 by comparison with a pre-set reference signal. The digitised signal is checked for 30 missing or marginal,pulses by the missing-pulse-detector lZ93(~1 ( (MPD) 46, and provides an enable signal indicating an edge or other feature of interest on the can. The leading edge of the MPD signal sets the start-pulse-detector latch (SPD) 48 and the trailing edge sets the end-pulse-detector 5 latch (EPD) 50. The new-line-detector 42 set by the SNL
40 indicates the start of a new scan line and is reset by the EPD 50 at the end of the first detected edge. Counter 51 is reset to zero by the leading edge of the NLD 42 and thereafter counts the CCD ca~era diode scan position for 10 that line. The contents of the counter are transferrd to - latch 54 by the SPD latch 48 in conjunction with the NLD
latch 42, thereby transferring the leading-edge coordinate of the can. Thereafter with the NLD latch reset, the EPD
latch 50 transfers successive trailing edge coordinates to latch 56 until, at the end of the line scan, latch 56 contains the coordinate of the far edge of the can.
Similarly counters 57 and 58 contain the width of the first and last edges of the can detected. Both counters are enabled by the MPD 46 and count clock pulses while the 20 MPD is active. Counter 57 counts the width of the leading edge while the NLD is active while counter 58 counts successive events when the NLD is reset, until the far edge width remains at the end of the scan line: each successive event in the line causes counter 58 to be reset by the SPD latch 48, although only the first and last ~- events in the line are associated with useful data, in-between events generally being spurious. In the event of a single edge being detected counter 58 will contain zero.
Data is transferred to the microcomputer 32 under control of the NLD latch 42. When the NLD 42 resets, an interrupt indicates that data in the latch 54 and counter 51 are ready for transfer. At the end of the scan line, or when NLD 42 goes active in the following scan line, another .
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interrupt indicates that data in the latch 56 and counter 5~ are ready for transfer. In the event of a single edge being detected the only interrupt will be at the end of the scan-line; if the contents of latch 54 is zero no edge 5 has been detected.
Referring now to Figure 3, the upper part of the illustration indicates a line scan 70 across a can top having a blemish 72 and the waveforms below indicate the resulting signals generated at the various logic circuit 10 components above described with reference to Figure 2.
Each waveform is marked to indicate the relevant component to which it relates. The measurement signals generated are:- a) the leading edge position in latch 54; b) the trailing edge position in latch 56; c) the width of rim at 15 the leading edge in counter 57; d) the widths of blemish and rim at the trailing edge in counter 58.
The computer 32 has stored therein reference values which set the limits for acceptance of the can with respect to distortions in shape and dimensional variations. If the 20 measurement signals fail to meet the set limits, a can ejector device may be automatically operated under computer control.
The preceding description relates to detection of simple ovality and dinting. However, it will be appreciated that 25 there can be two cameras (or a two dimensional camera or other equivalent) scanning the can in mutually transverse directions and that, during passage through the test station, a large plurality of scans are able to provide a large number or measurement signals to the computer. The 30 computer may be preset or programmed to process these signals cumulatively, and evaluate the shape and ~Z93(~51 dimensions of the can more precisely as to errors in shape and dimensions, for example having regard to algorithms stored in its memory.
Thus, errors in the edge rim of the can may be detected by 5 a) comparing the width of the rim at the leading and trailing edges; b) comparing change in rim widths between successive parallel scans; c) integrating the rim width measurements over an arc around the can and effecting a comparison of the integrated values. Analogously, by 10 monitoring the change in the leading and trailing edge positions through successive scans, it is possible to check for complex ovalities and other distortions from roundness which do not appear from a simple comparison of maximum diameters in two coordinate directions. In 15 general, ovality can be checked by:- a) comparing diameters in mutually perpendicular directions as above mentioned; b) checking that the maximum diameter is at the centre point of the perpendicular axis; c) checking that the median of the can, as measured on the appropriate 20 axis, has a constant position.
More generally, the above-described apparatus, incorporating a suitably dedicated or programmed computer, is capable of:-(a) determining deformation of an object by comparing maximum measurements in two perpendicular axes using two line-scan cameras, while items are in continuous motion on a conveyor;
(b) detecting deformation in an item which is symmetrical about the axis of motion, by measuring the width perpendicular to the axis of motion, lZ93(~t~i;1 determining the median of the object by determining the position of the two outside edges for successive scans and hence deviation of the median with respect to the axis of motion:
(c) detecting ovality of an object presenting a round face to the scanning cameras;
(d) determining width of edge(s) of object by scanning in one direction, memorising the width of the leading edge, then memorising width of successive events, resetting the width of each event on the detection of another feature until, at the end of the scan, the last event represents the width of the trailing edge;
(e) having determined succession of edge widths of an item, being able to compute deviations in the uniformity of the total edge surface for the whole item;
(f) using the scan in the axis parallel to the axis of motion to provide equal spaced scans in the other axis perpendicular to the axis of motion, thereby allowing intermittent or variable speed of the item along the conveyor;
(g) examining round items (in particular cans) for ovality;
(h) examining lipped items (in particular cans) for deformation of the lip.
A possible modification, in connection with features (g) .. _ .. _ . .. . . . . _ _, . . _ _ ... .. .... ............. _ . .... .... , .. . ............ , " ~, . .. ~ ., .,, , . ~
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above, is that of using two cameras scanning in parallel, one for detecting the beginning and one the end of a can rim.
, . . _ . . . . , . . , , _ . ., .......... , .. .... . ., ........ ~, .. .. .. . . .