A DEVICE FOR THE DETECTION OF ABNORMAL CONDITION OF A PORTION OF AN OBJECT WHICH IS MOVABLE RELATIVE TO THE DEVICE

Abstract: Arrangement for detection of an abnormal state of part of an object (5) moveable relative to the arrangement. The arrangement comprises a detector element (13) with an electrical conductor (19). An electrical signal occurs in the conductor depending on whether the detected part is in a normal or abnormal state. The arrangement has a self-guiding part (14) for guiding a detector electrode (19) in the self-guiding part in towards that part of the object (5) which is to be detected. In addition, the arrangement is resilient in a spring-like manner transverse to the feed direction of the object.

Description: A device for the detection of abnormal condition of a portion of an object which is movable relative to the device. Technical field: The present invention relates to an arrangement for detection of an abnormal state of part of an object moveable relative to the arrangement and comprising a detector element with at least one electrical conductor, in which an electrical signal occurs depending on whether the detected part is in a normal or abnormal state. Prior art : It is previously known to use relatively large detector electrodes to detect large surfaces of an object, in which respect no particularly great requirements are set on the position of the detector electrode relative to the object. However, large contact surfaces between object and detector create considerable interference problems. It is also known to use smaller detector elements with a relatively limited detector surface, which necessitates accurate tolerances in the object, or alternatively to provide the detector element with arrangements for displacement of the detector in accordance with the dimensions of the object. Technical problem: The aim of the present invention is to eliminate the abovementioned problems and to provide a very limited detector surface and at the same time ensure, by simple means, that the detector surface is at all times situated in the position where detection is to take place. Invention: The said aim is achieved by means of an arrangement according to the present invention, which is charac¬ terized in that the arrangement has a self-guiding part for guiding a detector electrode in the self-guiding part in towards that part of the object which is to be detected, and in that the arrangement is resilient in a spring-like manner transverse to the feed direction of the object. Description of Figures: The invention will be described in greater detail below on the basis of exemplary embodiments and with reference to the attached drawings, in which Figs. 1 and 2 show a perspective view and a plan view, respectively, of a complete detector arrangement in a first embodiment for detection of all four sides of an object. Fig. 3 is a diagrammatic section through line III-III in Fig. 2, Fig. 4 shows a section through the arrangement along line IV-IV in Fig. 2, Fig. 5 shows an extended view of a detector element included in the arrangement according to the invention in the first embodiments Fig. 6 shows a diagrammatic basic view of the detector element according to the invention, and Fig. 7 shows a cross-section through the detector element in a further embodiment. Preferred embodiments: Figs. 1 and 2 show the mechanical part of a complete detector installation according to the invention in a first embodiment consisting of four detector arrangements 1, 2, 3, 4 for detection of an abnormal state of an object. In the example shown, a circumferential welding seam along the edge sections 6 of a package 5 is detected. These edge sections run in a rectangular manner with pairs of edge sections opposite each other, .namely two longitudinal edge sections 7, 8 and two end edge sections 9, 10. The edge sections 7-10 are designed as protruding, laterally directed flanges and the welding seam is designed to seal a foil 11 to the flanges of the packaging container, which foil 11 covers the top of the package and thus seals the package content tight, a solid or viscous material which is electrically conductive and tends to leak out through the welding seam at defect points along the edge sections. In the example shown, the abnormal state is therefore a leakage through a weak point in a welding seam in the package. The arrangement comprises a control or indicating unit 12 in the form of a box placed alongside the conveyor belt on which the package 5 is fed past the detector installation. In the example shown, the box 12 forms an attachment for a detector element 13 in each detector arrangement. In the example shown, the detector installation consists of two detecting stations, a first station with two detector arrangements 1, 2 placed on either side of the advanced packages 5 for detecting the end edge sections 9, 10 of the package, and a subsequent station with two detecting arrangements 3, 4 for detecting the longitudinal edge sections 7, 8 of the package. Each of the detector arrangements 1-4 has the said detector element 13 which, in the example shown, is secured to the associated box 12 in such a way that the detector element extends in over the feed path along which the packages which are to be detected are fed. The detector elements 13 have a guiding part 14 which is supported in an elastically resilient manner so that the guiding part can be displaced in a spring-like manner in a transverse direction relative to the feed direction of the packages, which is indicated by arrows 15, 16. In addition, the guiding part 14 is designed to move in the vertical direction in order to adapt to different heights of packages 6 and, more specifically, the vertical posi¬ tion above the conveyor belt of that part of the package which is to be detected, in this case the edge sections 7, 8, 9, 10. In the example shown, the front end of the guiding part 14 is in the. form of a V since the guiding part is folded once about an essentially horizontal fold line 17 and can be displaced in a spring-like manner since the guiding part 14 is pivotable about an essentially vertical fold line 18 which, as a result of- an appropriate choice of material for the detector element, affords a spring-back function. The detector elements 13 are made for example of a semi-rigid plastic ■ film, expediently in the form of two plastic films welded together with an electrical conductor 19 lying between them. The front end of this conductor is positioned in the tip 20 of the V and is exposed there so that the conductor can come into conducting contact with that part of the package which is to be detected. Fig. 5 shows an example of a detector element in the extended state. This shows that, in addition to the guiding part, the detector element has an attachment part 21 at which the electrical conductor 19 leaves the detector element. Between the guiding part and the attachment part there is a narrowed part 22 by means of which the guiding part 13 is made moveable in the verti¬ cal direction in the assembled state of the arrangement, by means of which self-positioning is permitted. Fig. 6 shows more diagrammatically a detector element variant 23 which consists of a V-shaped recess 24 in a plate which is secured in a frame which is elastically resilient. Alternatively, the detector element itself can be elastically resilient, for example by being bent in such a way that it is angled relative to the transverse direction and is thus displaceable in spring-like manner relative to the package. The electrical conductor 25 is - exposed at its front end and is situated with this end at the tip 27 of the V-shaped recess 24. The arrows 28 and 29 symbolize the movement directions in which the detec¬ tor element moves during a guiding procedure, namely the transverse direction and vertical direction. By means of the guide edges of the detector element, a vertical component force occurs with the horizontal bearing force acting on the edge sections of the package, this vertical component force acting on the guiding part in such a way that the latter is guided in towards the tip of the V. This component must be greater than the force which holds the guiding part in the neutral vertical position which is assumed when the detector element is not acted upon by any package. When a package 6 arrives at the first detecting station with the two detector arrangements 1, 2, the latter are passed continuously and steplessly, in which respect the two detector elements 13 projecting into the path of the package are displaced by the edge sections of the package, in practice first by the corners of the package. In this respect the detector elements give way by pivot¬ ing about an axis 18, and when the end edge sections 9, 10 come into contact with the end of the guiding part 14, more particularly one of its two end edge sections 30, 31 converging towards the tip 20, the guiding part 14 is automatically positioned by means of the tendency of the detector elements to bear with spring force against the end edge sections 9, 10 in such a way that these pass the detector element at the tip 20 where the electrical conductor 19 is exposed. This emerges best from Fig. 3 and Fig. 4, where the guiding parts 14 have been guided in depending on the height of the package 6, more partic¬ ularly the vertical position of the edge sections. With reference to Fig. 4 it should be added that the arrange¬ ment includes an electrical circuit 32, 33 for each detector arrangement 1, 2, which circuit also includes the package and, more particularly, its inside, i.e " . its core, which is electrically conductive, while the shell is electrically insulating. The circuit includes a pole 35 which is placed under the advanced packages, for example under the conveyor belt 34 which supports the packages, this pole 35 forming a capacitive coupling to the core of the package. The circuit also includes a current source 36 and the control and indicating unit 12. Also connected to this is the electrical conductor 19, whose front end is exposed. The normal state for the package 6 is when the shell is completely closed and thus electrically insulating because the welding seam between the container part and covering foil of the package is complete, and the edge sections of the package are therefore electrically insulating. An abnormal state is when the welding seam is weakened or is not leakproof, and the contents have leaked out from the inside of the package, this being detected by means of the contents of the package coming into electrical contact with the free end of the conductor, in which respect the electrical circuit is closed, resulting in a change in the electrical mag¬ nitudes therein. This is indicated in a manner known per se by means of the control and indicating unit 12, for example by illumination of a signal lamp, activation of an acoustic signal or activation of a deflector following the detector station, which deflects the package to a container or branch line. The current in the electrical circuit can be direct current or alternating current. Furthermore, the current voltage and frequency can lie within wide limits. However, it is advantageous to select a voltage of such a level that flash-over can occur at the distance which can arise between the tip of the electrode and the contained goods, for example up to 30,000 V and 500 Hz. By means of the accurate guiding of the detector electrode which the free end of the electri¬ cal conductor 19 represents, it can be given a very small surface, which provides for a highly sensitive and interference-free detection. The downstream detecting station shown in Figs. 1 and 2 detects the longitudinal edge sections 7, 8 in a cor¬ responding manner by means of the packages being rotated 90° in a simple manner by striking against a round turning device 37 during the advance, which device forms a turning station. The packages are in this way advanced in their longitudinal direction and are fed between the two detector stations 3, 4. Fig. 7 shows a further variant of the detector element. here designated by 39. Its principle design, like the detector arrangement as a whole, can be the same as in Fig. 1. In co.ntrast, the detector electrode 40 of the detector element 39 is prolonged in such a way that it projects a distance from the V-shaped tip 41, which is formed by the two guiding parts 42, 43. In the example shown, the detector electrode is made up of a wire-shaped electrical conductor which extends out from the free end of the element at its tip 41. The electrode is advantage¬ ously made slightly resilient. The detector element 39 according to Fig. 7 is intended for objects 44 in which the part 45 which is to be checked is not situated in direct contact with the edge 46 of the object towards which the guiding edges 42, 43 of the detector element guide in the detector electrode 40. An example of this type of object is shown in Fig. 7 with a broken section of a package. In this case the edges 46 of the package against which the detector element is guided project beyond the elongate weld joint 45 between cover 47 and container part. The extended electrode 40 thus reaches a distance in under the edges of the cover, it being possible for the width of these edges beyond the weld joint 45 to vary somewhat without the detection function being impaired. A weak point or a leakage from the inner container space 49 of the con¬ tainer part 48 through the weld joint is detected by the same method as has been described above. In addition, as shown in Fig. 7, the flange 50 of the container part is often provided with a part 51 angled downwards from the edge 46 of the cover, as a result of which the package with this part also provides for a guiding of the electr¬ ode 40 for fine adjustment of the rough guiding which the detector element provides for in cooperation with the edge 46. The invention is not limited to the exemplary embodiments described above and shown in the drawings. For example, the detector elements can have another shape, for example for detecting a welding seam. However, the object must have a projecting edge so that guiding by means of the guiding part Is permitted. The electrical circuit can be formed by a coupling other than a capacitive coupling, ■ depending on the current type used and the electrical properties of the package contents. In principle a leakage detector can consist of a single detector arran¬ gement with one or more detector elements. In addition, these can be secured on a separate retainer and do not need to be secured to the ~ box 12. As a result of the spring-like self-adjustment, the detected part can vary along its length both in the vertical direction and in the lateral direction, for example it can be wave-shaped. Abnormal states other than leakage can be detected, such as weak points in a package part, which can result in altered electrical conditions. Detection in the case of packages with an air volume above the packed goods (so-called head space) can be carried out by means of the packages being turned and detected, if appropriate after shaking the goods down, in the upside-down state.

Claims: PATENT CLAIMS 1. Arrangement for detection of an abnormal state of part of an object (5) moveable relative to the arrangement and comprising a detector element (13) with at least one electrical conductor (19) , in which an electrical signal occurs depending on whether the detec¬ ted part is in a normal or abnormal state, characterized in that the arrangement has a self-guiding part (14) for guiding a detector electrode (19) in the self-guiding part in towards that part of the object (5) which is to be detected, and in that the arrangement is resilient in a spring-like manner transverse to the feed direction of the object. 2. Arrangement according to Patent Claim 1, charac¬ terized in that the self-guiding part has two guide edges (30, 31) which converge towards the detector electrode (19) and form an oblique angle to the said transverse direction, by means of which, due to the bearing pressure of the guiding part against the said part (6) of the object (5), a component force directed in the vertical direction is formed, which is designed to guide the detector electrode towards that part of the object which is to be detected. 3. Arrangement according to Patent Claim 2 for detection of a part (45) of the object (44), displaced relative to the part (46) towards which the detector element (39) is guided, characterized in that the detec¬ tor electrode (40) projects a distance from the guide edges (42, 43) towards the part (45) which is to be detected. 4. Arrangement according to Patent Claim 2 or 3, characterized in that the detector element (13) is elastically resilient in the vertical direction trans¬ verse to the feed direction in such a way that the self- guiding part (14) seeks to position itself in a neutral position in the vertical direction with component force directed in the vertical direction and below the com¬ ponent force in the vertical direction formed by the said bearing force. 5. Arrangement according to any one of the preceding* patent claims, characterized in that the guide edges (30, 31) of the guiding-part (14) are formed by a fold line (20) which merges at the guide edges together with the detector electrode (19) . 6. Arrangement according to Patent Claim 5, charac¬ terized in that the detector element (14) is made of an electrically insulating foil which is elastically resili¬ ent. 7. Arrangement according to Patent Claim 6, charac¬ terized in that the detector element (14) is designed with an attachment part (21) relative to which the guiding part (14) can bend in a spring-like manner about an essentially vertical fold line (18) . 8. Arrangement according to Patent Claim 1, charac¬ terized in that the arrangement forms part of an electrical circuit designed to be normally broken and to be closed when there is an abnormal state of the package (5), and in that the arrangement includes an indication unit for indicating an abnormal state. 9. Arrangement according to Patent Claim 8, in which respect the said abnormal state is a leakage of the package contents which are electrically conductive, characterized in that the said part (6) of the object is a good electrical insulator in the case of a normal state and a poor electrical insulator in the case of an abnormal state, in which respect the said circuit is closed via the detector electrode (19). 10. Arrangement according to Patent Claim 9, charac¬ terized in that the circuit includes a fixed pole (35) situated outside the package and designed to stand in capacitive contact with the core of the package. 11. Arrangement according to Patent Claim 8, charac¬ terized in that a voltage is applied across the detector electrode (19) and the core of the package (5), and in that the arrangement includes members for measuring the current change in the circuit, in which respect an abnormal state of the said part of the package is detect¬ ed by a change in the current strength. 12. Arrangement according to Patent Claim 7, charac¬ terized in that the detector element (13) is made up of two plastic films between which the detector electrode (19) is welded in such a way that its end is exposed at • the contact position of the guide edges of the guiding part.

Inventors: THORESON ANDERS, THORESON, ANDERS
Applicants: ALFASTAR AB
Application year: 1989
Main classification: G01M3
IPC codes: G01M3