A METHOD OF AND APPARATUS FOR OBTAINING AN INDICATION OF THE RELATIVE POSITIONING BETWEEN ARTICLES ON A CONVEYOR

Abstract: A succession of tins (A) to (F) move along a conveyor in the direction of an arrow (10). The tins each cross a beam emitted by a photocell (12). As the tins pass the beam from the photocell (12), the photocell is able to register either that a tin is blocking the beam or that there is no tin blocking the beam. A stream of pulses (14) are continually emitted, the frequency of which is proportional to the speed of the conveyor. When the photocell (12) detects that a tin is present, a counter counts alternate pulses, and the same counter counts every pulse when no tin is sensed. The combined count from the alternate pulses, when a tin is sensed, and each pulse, when a tin is not sensed, is compared with a predetermined value, and if the count is below the predetermined value an indication is given that the tins in their relative position are too close together.

Description: The present invention relates to a method of and apparatus for obtaining an indication of the relative positioning between articles on a conveyor. The present invention is particularly, although not exclusively applicable to obtaining an indication of the relative positioning between pans or tins on conveyors used in bakeries. In a bakery, the pans or tins containing dough are located on a conveyor which passes around turns within the heating or proofer section and the subsequent oven section. Each tin is able to pivot to a limited degree on the conveyor about its centre point, and the pans are located on the conveyor with different angles with respect to the centre line of the conveyor. If the pans are too close to each other then they may pivot and their corners will touch as the conveyor passes around a curve and the pans may fall off the conveyor or jam the machinery thus necessitating shut down of the production run until the blockage is cleared, with loss of production time and possible loss of at least part of the production run. In a prior proposal for checking the gaps between the turns a photocell has been used to measure the gap between the nearest portion of adjacent tins. Given that the tins are of oblong shape in plan view with their longitudinal axis extending across the conveyor, and given that the tins tend to pivot to a limited degree whilst on the conveyor, the smallest permitted gap between tins which is allowed must be that which corresponds to the most unfavourable orientation of the tins such as would give rise to jamming if the gap between the tins were not above a predetermined minimum. That most unfavourable orientation is when the longitudinal axis of the tins extends perpendicularly to the direction of movement of the conveyor. Thus where one or both of two adjacent tins do not extend straight across the conveyor, the photocell will give an alarm that the gap between them is too small, even though the centres of the tins may be sufficiently far apart for the tins to complete their journey on the conveyor satisfactorily. Consequently many false alarms may be given, or the minimum spacing between the tins greatly increased with the consequential loss of production rate. In U.S. Patent No. 4541624 (Sasage) there is shown a method of detecting whether the minimum interval between correctly aligned adjacent flat articles is above a minimal interval. As the flat articles which are stacked side by side are not always of the same length it is not possible to obtain a constant minimum distance between the flat articles merely by sending out articles at regular intervals. When no article is present at a location pulses are counted at a higher rate than when an article is present at that location and the combined sequential count of no article being present and an article being present is used to ensure that there is a predetermined distance between the flat articles. According to one aspect of the present invention, a method of obtaining an indication of the relative positioning between successive articles on a conveyor includes monitoring when the articles are passing a particular location and monitoring when an article is not passing that particular location, is characterlied in that first counting means are arranged to count at a different rate when an article is passing the particular location than when an article is not passing that particular location, with the combined count of the first counting means comprising, successively, the count when a first article is passing the particular location, the count when that first article has passed the particular location and the count when a second article is passing the particular location being used to provide an indication of the relative positioning between the articles. The relative positioning between the articles may be related to the gap between the articles, or the distance between the centres of the articles or any other desired spacing. With such a method, an indication of the effective spacing between articles which are irregular in shape and which may be at different relative angles may be obtained, with account being taken of the relative angles whereby it is not just the gap between the nearest points of adjacent articles which is measured. Thus, when comparing oblong baking tins, where the tins are at an angle to the direction of movement of the conveyor a lesser gap between the nearest portions of adjacent tins may be permitted whereas a greater minimum gap is required where the tins extend straight across the conveyor. The counting rate of the first counting means may be derived from a signal related to the speed of the conveyor. The different rates of the first counting means may comprise a lesser rate when an article is monitored as passing a particular location than when an article is not passing that location. The combined count at the different rates may be compared to a control count in order to provide an indication of the relative positioning between the articles. The first counting means may count pulses, and a different number of pulses may be counted for a set time period to achieve the different rates. The method may further comprise using a second counting means arranged to count at a different rate when an article is passing a particular location than when an article is not passing that particular location, with the combined count of the second counting means at different rates comprising, successively, the count when an article is passing a particular location, the count when that article has passed the particular location and the count when the next article is passing the particular location being used to provide an indication of the relative positioning between alternate successive articles to those articles which the first counting means provides an indication of the relative positioning between. According to another aspect of the present invention apparatus for obtaining an indication of the relative positioning between successive articles on a conveyor includes monitoring means arranged to monitor when an article is or is not passing a particular location and first counting means arranged to count at a different rate when an article is passing the particular location than when an article is not passing that particular location, is characterised in that means are provided which are adapted to combine the sequential count obtained when a first article is passing a particular location, when that article has passed the particular location and when the next article is passing the particular location and means are adapted to use the combined sequential count of the first counting means at the different rates to provide an indication of the relative positioning between the articles. The counting rate of the first counting means may be arranged to be provided or derived from a rate relating to the speed of the conveyor. The apparatus may include a second counting means arranged to count at a different rate when an article is passing a particular location than when an article is not passing that particular location, with means being provided which are adapted to combine the sequential count obtained when an article is passing a particular location, when that article has passed the particular location and when the next article is passing the particular location, with that combined count of the second counting means being arranged to provide an indication of the relative positioning between alternate successive articles to those articles which the first counting means are arranged to provide an indication of the relative positioning between. The invention may be carried into practice in various ways, but one embodiment will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a succession of tins passing along a conveyor, and Figure 2 is a schematic diagram of the sequences of operation. As shown in Figure 1, a succession of pans or tins A to F each containing dough move along a conveyor (not shown) in the direction of an arrow 10. The tins each cross a beam emitted by a photocell 12 on their way to a proofer, for proofing, and subsequently to an oven for cooking. In the proofer and oven stages the conveyor travels around bends, and it is essential that the tins do not contact each other, as such contact can result in the tins jamming the conveyor. Each tin is generally oblong in plan view and their longer axis extends across the direction of travel. Each tin is able to pivot on the conveyor about its centre point in either direction relative to the direction of travel so that the angle of the longitudinal axis of the tins to the normal to the direction of travel is within 25° on either side of that normal. Consequently the gap between two tins whose longitudinal axes are coincident with that normal (such as the tin D) must be greater than the gap between two tins whose longitudinal axes are at an angle to that normal if contact between the tins during their passage around the bends is to be avoided. Thus it is the spacing between the centres of the tins which is important or their relative positioning rather than a set distance between the tins regardless of their orientation. As the tins pass the beam from the photocell 12, the photocell is able to register either that a tin is blocking the beam or that there is no tin blocking the beam. The output from the photocell 12 is shown in Figure 2, plotted against time, with the raised portions corresponding to a tin crossing the beam. A stream of pulses 14 are continually emitted, and those pulses 14 are derived from the main jackshaft of the conveyor through a toothed sprocket. One pulse is emitted during the passing of one tooth of the sprocket past a magnetic sensor, and each pulse thus corresponds with a precise movement of the conveyor (in this case 0.01 inches). As the jackshaft is directly coupled to the conveyor by timing belts, slip between these parts is impossible and thus the pulses 14 correspond to the exact rate of movement of the conveyor from stationary to full speed, no matter how fast or slow that change may be. It will be appreciated that the frequency of pulses shown in Figure 2 has been shown schematically only, and in practice the frequency would be far greater. Two counters 16 and 18 are provided, each of which are arranged to count alternate pulses when a tin is sensed by a photocell, and every pulse when no tin is sensed. The rate of counting of pulses by the counters 16 and 18 is illustrated by the line 20. In use, the counter 16 is initiated when the first portion of the tin A is sensed, and alternate pulses are counted until the tin A passes the photocell. Then the counter 16 records every pulse until the first portion of tin B is sensed whereupon alternate pulses are again counted until the end of tin B passes the photocell. At that time, the number of counts in the counter 16 is compared with a predetermined value, and if it is below that predetermined value an output will be given which either stops the conveyor or gives an alarm or both in order to enable the spacing to be adjusted. It will be appreciated that, as the frequency of the pulses counted is related to the speed of the conveyor, an accurate indication of the relative positioning between the tins can be obtained regardless of the speed of the conveyor and without the need to alter the predetermined value. The counter 16 continues to count until the beginning of the tin C is sensed whereupon the counter is reset and commences counting again until the end of the tin D passes the photocell, at which time its count is again compared to the predetermined value as previously described. The counter 16 also counts from the beginning of the tin E to the end of the tin F. Thus the counter 16 measures, or provides an indication of the spacing or relative positioning between the tins A and B, C and D, and E and F. The counter 18 is reset when the beginning of the tin B is sensed and counts in the way previously described in relation to the counter 16 until the end of the tin C passes the photocell at which time its count is compared to the predetermined value with the same consequence occurring if the level of the count is below the predetermined value as previously described in relation to the count of the counter 16. When the photocell senses the beginning of the tin D, the counter 18 is reset and the count commences again as previously described until the count is compared with the predetermined value when the rear of the tin E passes the photocell. Thus the counter 18 measures, or provides an indication of the spacing or relative positioning between the tins B and C, and D and E. Should the conveyor stop then, as all data relevant to the counters 16 and 18, the pulses from the speed of the conveyor and the predetermined level are fed to and stored in a programmable logic controller unit, when the conveyor is restarted continuation of measurement can be resumed from precisely where it left off.

Claims: 1. A method of obtaining an indication of the relative positioning between successive articles (A, B, C, D, E, F) on a conveyor including monitoring when the articles are passing a particular location and monitoring when an article is not passing that particular location, characterised in that first counting means (16) are arranged to count at a different rate when an article is passing the particular location than when an article is not passing that particular location, with the combined count of the first counting means comprising, successively, the count when a first article is passing the particular location, the count when that first article has passed the particular location and the count when a second article is passing the particular location being used to provide an indication of the relative positioning between the articles. 2. A method as claimed in Claim 1 in which the counting rate of the first counting means is derived from a signal related to the speed of the conveyor. 3. A method as claimed in any preceding claim in which the different rates of the first counting means comprise a lesser rate when an article is monitored as passing a particular location than the rate when an article is not passing that location. 4. A method as claimed in any preceding claim in which the combined count at the different rates is compared to a control count in order to provide an indication of the relative positioning between the articles. 5. A method as claimed in any preceding claim in which the first counting means counts pulses, and a different number of pulses is counted for a set time period to achieve the different rates. 6. A method as claimed in any preceding claim comprising using a second counting means (18) arranged to count at a different rate when an article is passing a particular location than when an article is not passing that particular location, with the combined count of the second counting means at the different rates comprising, successively, the count when an article is passing a particular location, the count when that article has passed the particular location and the count when the next article is passing the particular location being used to provide an indication of the relative positioning between alternate successive articles to those articles which the first counting means provides an indication of the relative positioning between. 7. Apparatus for obtaining an indication of the relative positioning between successive articles on a conveyor including monitoring means arranged to monitor when an article is or is not passing a particular location and first counting means arranged to count at a different rate when an article is passing the particular location than when an article is not passing that particular location, characterised in that means are provided which are adapted to combine the sequential count obtained when a first article is passing a particular location, when that article has passed the particular location and when the next article is passing the particular location and means are adapted to use the combined sequential count of the first counting means at the different rates to provide an indication of the relative positioning between the articles. 8. Apparatus as claimed in Claim 7 in which the counting rate of the first counting means is arranged to be provided or derived from a rate relating to the speed of the conveyor. 9. Apparatus as claimed in any of Claims 7 or 8 including a second counting means arranged to count at a different rate when an article is passing a particular location than when an article is not passing that particular location, with means being provided which are adapted to combine the sequential count obtained when an article is passing a particular location, when that article has passed the particular location and when the next article is passing the particular location with that combined count of the second counting means at the different rates being arranged to provide an indication of the relative positioning between alternate successive articles to those articles which the first counting means are arranged to provide an indication of the relative positioning between.

Inventors: MORLEY, GARY
Applicants: TWEEDY OF BURNLEY LIMITED
Application year: 1988
Main classification: B65G43
IPC codes: B07C1, B07C5