OPTICAL INSPECTION SYSTEM FOR PREFORMS

Abstract

It is proposed to carry out an optical inspection of preforms (7) by means of at least one camera device (2, 3, 13), in such a way that the preforms (7) are in a relative position to each other that is unchanged in comparison with the injection molding operation.

Claims

1. Method for optical inspection of hollow bodies, in particular preforms, by means of at least one camera device, wherein the hollow bodies, in particular preforms, are examined in an unchanged relative position to each other with respect to an injection molding operation.

2. Method according to claim 1, wherein the mouth regions and/or threaded regions of the hollow bodies, in particular preforms, are examined, in particular examined preferentially and/or more precisely and/or with higher resolution and/or more intensely and/or for other features and/or for a greater number of features.

3. Method according to claim 1, wherein during at least part of the optical inspection process the hollow bodies, in particular preforms, are still located inside at least part of the injection mold, in particular by their end opposite the mouth region and/or threaded region.

4. Method according to claim 1, wherein during at least part of the optical inspection procedure the hollow bodies, in particular preforms, are located outside the injection mold, in particular are located at least in part within a removal device for removal of hollow bodies, in particular preforms, out of the injection mold and/or are located at least in part in a transfer device for transfer of hollow bodies, in particular preforms, from one position to another position.

5. Method according to claim 4, wherein during at least part of the optical inspection operation the hollow bodies, in particular preforms, are gripped in the area of the mouth region and/or threaded region, in particular on their inner side.

6. Method according to claim 1, wherein the at least one camera device is moved, in particular between a resting position of the at least one camera device and an optical inspection position of the at least one camera device, and/or during the optical inspection operation.

7. Method according to claim 1, wherein the optical inspection takes place from different directions and/or in oblique inspection, in particular in relation to the longitudinal axis of the hollow bodies, in particular preforms, and/or in relation to the longitudinal axis of the threaded region of the hollow bodies, in particular preforms.

8. Method according to claim 1, wherein the optical inspection takes place using at least one camera device and/or using at least one reflection device, in particular takes place using at least one mirror device.

9. Method according to claim 1, wherein the optical inspection method is carried out using at least one illumination device.

10. Method according to claim 1, wherein at least one camera device is designed as digital camera device and/or numerical analysis methods are used for analysis of the optical information obtained by means of the at least one camera device.

11. Method according to claim 10, wherein output data are generated which can be used in particular for follow-up control of the injection molding operation.

12. Optical inspection system for hollow bodies, in particular preforms, having at least one camera device for photographing surface areas of the hollow bodies to be inspected, in particular preforms, wherein it is designed and set up in such a way that it carries out an optical inspection method according to claim 1.

13. Optical inspection system according to claim 12, characterized by at least one digital camera device, whereby the at least one digital camera device is movably and/or rigidly disposed.

14. Optical inspection system according to claim 12, characterized by at least one gripping device for removal of hollow bodies, in particular preforms, from at least one part of an injection mold and/or for transfer of hollow bodies, in particular preforms, between two positions.

15. Optical inspection system according to claim 12, characterized by at least one programmable control unit for control of the components of the optical inspection system and/or for analysis of the information obtained from the at least one camera device and/or for calculation of output data, which can be used in particular for follow-up control of the injection molding operation.

Description

[0026] Further details of the invention and in particular embodiments, given by way of example, of the proposed device and of the proposed method will be explained in the following with reference to the attached drawings.

[0027] FIG. 1 shows an injection molding machine with a first embodiment example of an optical inspection system for carrying out an optical inspection method in different views and positions;

[0028] FIG. 2 shows a second embodiment example of an optical inspection system for carrying out an optical inspection method in schematic lateral plan view;

[0029] FIG. 3 shows a third embodiment example of an optical inspection system for carrying out an optical inspection method in schematic lateral plan view;

[0030] FIG. 4 shows an injection molding machine with a fourth embodiment example of an optical inspection system for carrying out an optical inspection method in different views and positions.

[0031] Shown respectively in FIG. 1 in schematic top view is an injection molding machine 1 with optical inspection system 2 in the form of a camera array 3 from different viewing directions. The injection molding machine 1 has here a split injection mold 4, 5, which consists of a plurality of injection mold parts 4, 5, which can be moved in a way relative to one another and above and beyond this can, if need be, be moved within themselves. Especially for the molding of a thread 6 for the preforms 7 (only partially visible, respectively, in FIG. 1), usually required is a multi-part injection mold part 5, movable within itself. Such injection mold parts 4, 5 are known per se in the state of the art and are therefore not described in detail, for reasons of conciseness. The relative maneuverability of the two injection mold parts 4, 5 of the injection mold 1 is moreover indicated by a double arrow in FIG. 1. Mentioned for the sake of completeness is that in the top view of FIG. 1a one injection mold part 5 of the injection mold 4, 5 is not shown, for reasons relating to technical drawing. The affected injection mold part 5, on the other hand, is to be seen in the lateral plan views according to FIG. 1b and FIG. 1c (in addition to the injection mold part 4).

[0032] The injection mold 4, 5 is designed in such a way that a plurality of preforms 7 can be produced in a single injection molding operation. In the present example, the cavities 8 for formation of the preforms 7 are designed as a type of matrix of, here, four lines and six columns. Of course dimensions differing therefrom are also conceivable. Also the configuration of the individual cavities 8 is not limited to a rectangular grid.

[0033] To form the preforms 7, the injection mold parts 4, 5 of the injection mold are placed flush on one another and plastic material (in the food sector often PET=polyethylene) is injected in heated, as a rule semifluid, form into the cavities 8 of the injection mold 4, 5 under high pressure. Serving to form a hollow space in the preforms 7 are corresponding male forms, which are provided in the top 5 of the injection mold 4, 5. In FIG. 1 these are situated in a retracted position and are therefore not visible.

[0034] After the preforms 7 have been formed and have cooled off sufficiently, the injection mold 4, 5 is opened by opening the two injection mold parts 4 and 5.

[0035] As soon as the injection mold parts 4, 5 have moved sufficiently apart, a slide 10, drivable by means of an actuator 9, is driven into the formed interim space between the two injection mold parts 4, 5. The slide 10 was located during the actual injection molding operation here on the side with respect to the closed injection mold 4, 5 (comparable in particular also with FIG. 1a). The actuator 9 is indicated only schematically here. Appropriate here is, for example, a linear motor or a servomotor/stepping motor, which can drive the slide 10 linearly, for example by means of a toothed rack.

[0036] The slide 10 consists here of two main components connected firmly to one another, namely the actual optical inspection system 2 and a removal gripper 11, which, with the aid of various gripping elements 12 (see FIG. 1c), is able to take the finished preforms 7 out of the respective mold part 4. Owing to the selected perspective of FIG. 1a only the back sides of the optical inspection system 2 and of the removal gripper 11 are to be seen, so that no details can be discerned.

[0037] Shown schematically in FIG. 1b in lateral plan view is the carrying out of the inspection operation. As can be seen from FIG. 1a, the optical inspection system 2 here is designed comparatively narrowly and in particular does not have the same dimensioning as that of the injection mold components 4, 5. This is for cost reasons since in this way the number of digital cameras 13 of the digital camera arrays 3 can be reduced. Also the necessary travelling distances of the entire slide 10 can usually be thereby reduced, which can bring both space savings as well as savings in time in operation. In particular the digital cameras 13 of the camera array 3 are disposed in such a way that at a given point in time only a portion of the injection mold part 4 and thereby only part of the finished preforms 7 can be optically inspected. For example, at a given point in time only one or two columns of the preform configuration can be inspected.

[0038] Drawn here in FIG. 1b is a digital camera array 3 of two digital cameras 13. Based on the indicated fields of vision of the individual cameras 13, it can be seen that the threaded region 6 of the preforms 7 can be optically inspected. Owing to the different viewing directions of the two digital cameras 13, different sides can be inspected, so that altogether the entire threaded region 6 of each preform 7 is visible. To increase the inspection quality it is of course also conceivable that three or four digital cameras 13 are disposed, of which each has to optically inspect a sector of at least 120 (three digital cameras 13) or respectively 90 (four digital cameras 13) (of course a greater number of digital cameras 13 is possible, whereby the sector becomes correspondingly smaller). In reality it of course makes sense to provide for a certain overlap between the individual picture areas in order, on the one hand, to increase the quality of the optical inspection, on the other hand to compensate for certain position tolerances, in particular also based on vibrations. The overlapping picture area, for example, can amount to up to 5, 10, 15, 20, 25 or 30 (or another magnitude).

[0039] For the sake of completeness it should still be mentioned that of course an increased number of digital cameras 13 of the camera array 3 can thereby arise in that the fields of vision of the individual digital cameras 13 are selected in such a way that they do not examine any complete column of preforms 7, but rather only part of a column (if necessary also only an individual preform 7). The required depth of field of the picture can thereby be reduced so that simpler optics can be used for the digital cameras 13 and/or the resolution of the obtained picture (of the obtained pictures) can be increased so that the quality of the optical inspection can increase further.

[0040] Thus while the slide 10 is driven linearly, the optical inspection system 2 sweeps gradually over the injection mold part 4 with the preforms 7 located therein, so that altogether a complete image results. The obtained picture data are transmitted to a computer (or another programmable device), where they are analyzed for any flaws using generally known algorithms.

[0041] The advantage with this proposed method here consists in that the preforms 7 are located exactly in the relative position with respect to one another in which they were injection molded. Thus, upon discovery of a defect, the cavity 8 in the injection mold 4, 5, in which the defect has occurred can be clearly determined. It is possible that by changing the process parameters the occurrence of the defect in future preforms 7 can thereby be prevented, if necessary, in an automated way. Even if a manual intervention should be required, it would not be necessary first to carry out a search for the defective cavity 8, so the maintenance time can be reduced and thus the downtime of the injection molding machine 1 can be clearly reduced where applicable. A correspondingly increased productivity is the result.

[0042] The slide 10, which is driven out of the resting position shown in FIG. 1a in the direction of the opened injection mold 4, 5, moves afterwards continuously further until the removal grippers 11 with the individual gripping elements 12 (see FIG. 1c) are located in a removal position, which is situated opposite the corresponding injection mold part 4. This position is shown in FIG. 1c.

[0043] As soon as the position is reached, the removal gripper 11 is driven in the direction of the opened injection mold part 4 (lowered), so that the gripping elements 12 can seize the individual preforms 7 on their inner side. Then the removal gripped 11 is withdrawn (lifted) and the preforms 7 are pulled out of the cavities 8 of the respective injection mold part 4. This plunging and pulling out movement is indicated in FIG. 1c by a double arrow.

[0044] After removal of the preforms 7 out of the injection mold part 4, the individual preforms 7 stick on the corresponding gripping elements 12 of the removal gripper 11, so that a configuration in the sense of FIG. 2 results. Then the slide 10 with the removal gripper 11 is driven back in the direction of the resting position, so that the space between the two injection mold parts 4, 5 becomes free again and a new injection molding production cycle can begin.

[0045] The preforms 7 located on the gripping elements 12 of the removal gripper 11 can then be transferred to a further transfer element in an ordered way, or can also be ejected randomly into a collecting box, however (usually a plurality of collecting boxes, such as (at least) one box for defect-free preforms 7, as well as (at least) one collecting box for defective preforms 7). Both are basically known and are not shown here.

[0046] As can be gathered from FIG. 1, the additional time and effort involved with the optical inspection method proposed here is astonishingly minimal. In particular no additional acceleration or braking procedures are required. The sole difference to a normal removal gripper 11 without optical inspection device consists in that here a slide 10 with a certain extension in the form of an optical inspection system 2 must be provided. This has as a result that, on the one hand, the travelling distance of the slide 10 has to be selected to be a little longer (to compensate the dimension of the optical inspection system 2 and its attachment); above and beyond this are somewhat greater masses to be moved (i.e. in particular to accelerate and brake). In relation to the removal gripper 11, however, the optical inspection system 2 has usually a comparatively minimal mass, so that this effect is usually negligible. But also the time loss from the additional travelling distance is usually minimal with today's travel speeds. To name typical values: while the actual injection molding operation with closed injection mold 4, 5 lies in a time range of at most 10 to 30 seconds, the time loss from the additional travelling distance is in the range of secondand thus almost completely negligible.

[0047] Shown schematically in a lateral plan view in FIG. 2 is a further embodiment of an optical inspection system for carrying out an optical inspection method. Here the removal gripper 11, on whose gripping elements 12 the preforms 7 are located, is moved linearly past a camera array 3 of a plurality of digital cameras 13, whereby the camera array 3 is rigidly mounted.

[0048] The optical inspection step according to FIG. 2 can, on the one hand, be carried out in addition to the optical inspection according to the embodiment example according to FIG. 1, so that now also the hollow cylindrical region of the preforms 7 (remote from the threaded region 6 of the preforms 7) can be optically inspected. This is in particular of advantage since the preforms 7 are still within the respective injection mold parts 4 during the optical inspection method according to FIG. 1 and are thus not <completely> visible. The optical inspection can thereby be complemented to a certain extent.

[0049] It is however also conceivable that an optical inspection is carried out exclusively with a configuration according to FIG. 2. The digital cameras 13 of the camera array 3 are then positioned in such a way that in particular they are also able to catch the threaded region 6 of the preforms 7. As a rule, appropriate therefor is that the axes of vision of the individual digital cameras 13 are selected in such a way that they do not lie parallel to the lines or respectively columns of the cavities 8 of the injection mold part 4, 5 or respectively the configuration in lines or respectively columns of the gripping elements 12 of the removal gripper 11. With preforms 7 spaced sufficiently apart from one another it is then absolutely possible to inspect the preforms 7 optically, in particular also their threaded regions 6, even if this seems impossible with the selected simplified drawn representation in FIG. 2.

[0050] As a general rule, however, it is advantageous if an inspection method in the sense of FIG. 1 is combined with an inspection method in the sense of FIG. 2 (i.e. an optical inspection from different directions with respect to the longitudinal axis of the preforms 7 takes place so that these are able to be inspected optically in an especially precise way over their entire length). Of course optical inspection methods differing from FIG. 1 and/or from FIG. 2 can also be used.

[0051] Shown in FIG. 3 is a further optical inspection system 14. In order to reduce the number of digital cameras 13, in the optical inspection system 14 shown in FIG. 3 a plurality of mirrors 15 are attached to a basic element 17 by means of suitably disposed and dimensioned supporting rods 16, whereby the basic element 17 also supports the digital cameras 13. The optical inspection system 14 can be used, for example, instead of the optical inspection system 2 according to FIG. 1.

[0052] As can be seen, the individual mirrors 15 are arranged in such a way that the entire field of vision of the digital camera 13 can encompass both the front sides and the back sides (referring to the placement of the digital camera 13) of the threaded region 6 of the preforms 7. A reduced number of digital cameras 13 can thereby be sufficient.

[0053] Of course in an analogous way to what was said in relation to FIG. 1, it is also possible that a digital camera 13 is not responsible for a complete column of preforms 7, but instead respectively for just a lesser number of preforms 7 (if necessary also for just one single preform). The required depth of field can thereby be reduced, which has already been discussed. This of course does not apply just for the embodiment example shown in FIG. 3, but also for the embodiment example shown in FIG. 2 as well as for other embodiments not shown here of an optical inspection system.

[0054] Only for reasons of completeness it is pointed out that a plurality of mirrors 15 can be provided per preform 7, so that, for example, by means of a direct camera view and two mirrors, a sector of 120 can be inspected in each case (typically plus safety margin, as already mentioned).

[0055] Shown in FIG. 4 is a variation of the method shown in particular in FIG. 1 or respectively of the device shown there.

[0056] Here the injection mold opens with the injection mold parts 4, 5 after the actual injection molding operation in such a way that the bodies of the preforms 7 (the region of the preforms 7 opposite the respective threaded area 6) after the opening of the injection mold protrude outwardly, while the preforms 7 are still located with their threaded regions 6 in the respective injection mold part 4 or 5 (and are held there).

[0057] The removal gripper 11 is then moved by the actuator 9 (see FIG. 4a) over the respective injection mold part (here 4) and takes the preform out of the injection mold part 4. The removal gripper 11 can thereby be designed in an advantageous way as vacuum-applied removal gripper 11 (which has a plurality of cavities 8 for receiving body regions of the preforms 7, to each of which a partial vacuum or a vacuum can be applied, and thus are able to hold the respective preform 7 in position).

[0058] The optical inspection then takes place according to FIG. 4b by means of the optical inspection system 2, which has one or more digital cameras 13, whereby the optical inspection system 2 is positioned opposite the removal gripper 11 (through movement of the optical inspection system 2 and/or through movement of the removal gripper 11). The threaded regions 6 (and moreover also the mouth regions) of the preforms 7 can then be optically inspected in an especially advantageous way.

[0059] Furthermore, the preceding description, in particular the description given with respect to FIG. 1, applies in an analogous way also to the present embodiment example according to FIG. 4.