Capping method for capping containers by means of screw caps, and electronic capping machine for implementing the method

Abstract

In a capping method wherein screw caps (10) are applied to containers (11), the starting positions of the threads (12, 13) of the cap (10) and the container (11) are detected and the application angle of a cap (10) is measured by using the starting positions of the threads (12, 13) detected. In an embodiment of the method, the passage of the cap (10) through a predetermined position (F) reached by the cap (10) before completion of its tightening on the container (11) is detected, and a function relating the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13) is determined by executing, in a calibration phase, a plurality of sequences of capping cycles where each sequence exploits a different starting offset of the threads (12, 13), and by detecting the passage of the cap (10) through the predetermined position (F) in all cycles of all sequences.

Description

[0001] CAPPING METHOD FOR CAPPING CONTAINERS BY MEANS OF SCREW CAPS, AND ELECTRONIC CAPPING MACHINE FOR IMPLEMENTING THE METHOD

[0002] Technical Field

[0003] This invention relates to the handling and packaging of liquids, and more particularly it concerns a capping method for applying screw caps to containers where the cap application angle is monitored and an electronic capping machine for implementing the method.

[0004] Background Art

[0005] In capping machines for applying screw caps the operation of capping a container (by way of example, hereinafter reference will be made to a bottle) requires that the cap simultaneously performs a rotary motion and a vertical translational motion. In electronic capping machines, at least the rotary motion is imparted by an electrical motor from which information can be obtained allowing determining some of the parameters of interest for the capping operation, in particular the torque applied to the cap. The vertical translational motion can be imparted by a mechanical cam or by a linear electrical motor. In the latter case ("full servo" capping machines) it is possible to obtain also from the linear motor information allowing determining other parameters of interest for the capping operation, e.g. the vertical position of the cap and the force applied to the cap. The whole of this information is useful for monitoring the capping quality during operation of the capping machine.

[0006] A quantity used in such monitoring is the so called "application angle" (or pull-up angle), that is the angle by which the cap is rotated from the instant of mutual engagement between the threads of the cap and the bottle until the complete cap tightening. The position of complete cap tightening during a working cycle concerning a given kind of bottle is not constant, since it depends on the instant of mutual engagement between the threads of the cap and the bottle, on the starting offset condition of such threads and on the instant the tightening torque is attained. Such a position can range from a minimum value MIN to a maximum value MAX, which define a range characterising a good capping. Therefore, the application angle too will fall within a certain range. For instance, a cap with a single-start thread may typically have a nominal application angle of the order of 720° and an acceptable application angle could then range from 680° to 740°. Monitoring is intended to check that the application angle falls within the acceptable range of values. In case of mechanical capping machines, often a random measurement of the application angle is made on already capped bottles, by performing a manual or automated check based on the detection of notches provided on the cap and the bottle and identifying the angular positions at which the threads start.

[0007] Instead, in an electronic capping machine it is possible to monitor the application angle during cap application, by exploiting the information that can be obtained from the motor(s), and this allows an early detection of possible operation faults of the capping machine.

[0008] A measurement technique utilisable in electronic capping machines where only the rotary motion is motor driven can exploit the information on the electromagnetic torque applied to the cap. Typically, during capping, the motor driving the head rotation is operated at a speed depending on the production rate of the packaging installation and the motor current, which is related to the electromagnetic torque applied, is monitored. When the torque attains a value set by the operator, it is possible to slow down the motor and to end the tightening phase at a speed different from the previous one.

[0009] A problem with this technique is that the torque signal must be scarcely affected by noise in order to enable a precise detection of the attainment of the slow-down torque. Moreover, a precise detection of the engagement between the threads is not possible, since the slow-down position is not necessarily related to that engagement.

[0010] Capping methods for electronic capping machines have already been proposed in which the start of the threads is detected by detecting the passage of the cap through a predetermined position. For instance, JP H6115591 A, FR 3076551 Al and JP 2020147303 A disclose methods in which, during capping, the cap, after having been brought into engagement with the bottle, is lifted again by rotating in opposite direction to the screwing direction (counterrotation) up to the thread starting position, where the contact between the threads ceases and an abrupt cap fall takes place. The position at which the fall starts is stored as the thread starting position.

[0011] Such known methods have a number of drawbacks. In particular, carrying out a counterrotation during the normal capping operations significantly increases the duration thereof and limits performance of the capping machine. Moreover, in case of threads of which the cross sections are not squared but are tapered both on the bottle and the cap (this being the usual situation) the cap fall could take place before the start of the threads, thereby making the known methods inaccurate. Moreover, JP 2020147303 A concerns capping machines where the translatory motion is driven by a cam, and therefore it requires use of dedicated position or displacement sensors for detecting the head fall, thereby making the capping machine complex.

[0012] EP 4223689 Al discloses another capping machine in which the starting positions of the threads of a cap and a container are detected.

[0013] Summary of Invention

[0014] It is an object of the present invention to provide a capping method and a "full servo" capping machine for implementing the method that obviate the drawbacks of the prior art and enable a reliable monitoring of the application angle.

[0015] This object is achieved by a method including, for each container being capped, the steps of:

[0016] - analysing, on the basis of information supplied at least by the motor imparting the translational motion to the cap, the evolution of the vertical position of the cap during at least part of a capping operation and optionally detecting, during the analysis, the passage of the cap through a predetermined position;

[0017] - determining a function representative of the evolution of the vertical position of the cap and optionally a function that relates the passage of the cap through the predetermined position to the starting positions of the threads and that is obtained in a calibration phase by processing information supplied by the motors imparting the rotary and translational motions to the cap;

[0018] - determining the starting positions of the threads by using either the function representative of the evolution of the vertical position of the cap or the function relating the passage of the cap through the predetermined position to the starting positions of the threads; and

[0019] - measuring the rotation performed by the cap from the starting positions of the threads thus determined until completion of the capping.

[0020] In an embodiment in which the evolution of the vertical position of the cap is analysed, the analysis of such evolution and the extraction of the starting positions of the threads are performed by means of a neural network.

[0021] In an embodiment in which the passage of the cap through a predetermined position is detected, such a position is either a position reached by the cap before completion of its tightening on the container or the position where the first contact between a cap and a container occurs.

[0022] In the first case, the passage of the cap through the predetermined position is detected in each cycle of a plurality of sequences of capping cycles where each sequence is executed with a different relative starting angular position of the threads.

[0023] In the second case, the passage of the cap through the position of first contact between a cap and a container is detected in each cycle of a plurality of cycles of head displacement each including lifting the cap from the first contact position up to a position of loss of contact with the container and bringing it again to the first contact position with a different relative angular position of the cap and the container.

[0024] A "full servo" capping machine for implementing the method includes means for processing information supplied by the motors simultaneously imparting to a cap the rotary motion about an axis and the vertical translational motion along the same axis required by the capping, which means are programmed for:

[0025] - analysing the evolution of the vertical position of the cap during at least part of a capping operation and optionally detecting, during the analysis, the passage of the cap through a predetermined position;

[0026] - determining a function representative of said evolution and optionally a function that relates the passage of the cap through the predetermined position to the starting positions of the threads and that is obtained in a calibration phase of the processing means by processing information supplied by the motors imparting the rotary ands translational motions to the cap;

[0027] - determining the starting positions of the threads by using either the function representative of the evolution of the vertical position of the cap or the function relating the passage of the cap through the predetermined position to the starting positions of the threads; and

[0028] - measuring the rotation performed by the cap from the starting positions of the threads thus determined until completion of the capping.

[0029] Brief Description of Drawings

[0030] The above and other features and advantages of the present invention will become apparent from the following description of preferred embodiments made by way of nonlimiting example with reference to the accompanying drawings, in which:

[0031] - Fig. l is a block diagram of a capping machine according to the invention;

[0032] - Fig. 2 is a flow chart of a first embodiment of the method according to the invention;

[0033] - Fig. 3 is a graph illustrating the principle on which that first embodiment is based;

[0034] - Fig. 4 is a schematic representation of the relative vertical position of the cap and the bottle explaining the principle on which a second embodiment of the method according to the invention is based; - Fig. 5 is a flow chart of the second embodiment of the method; and

[0035] - Fig. 6 is a graph illustrating a step of the flow chart depicted in Fig. 5.

[0036] Description of Embodiments

[0037] Referring to Fig. 1, a "full servo" electronic capping machine 1 according to the invention includes, in usual manner, a plurality of capping heads 2a. . ,2n (hereinafter simply referred to as "head(s) 2" where, as shown for head 2a, the rotary motion about the axis and the vertical translational motion along the axis required for the capping are imparted to shaft 20 carrying cap-holding cone 21 by respective electrical motors 22R, 22L controlled by a control unit 3. Information allowing determining some parameters of interest for monitoring the capping operations can be obtained from electrical motors 22R, 22L, in particular electromagnetic torque delivered, rotation speed and angular position of each head 2 as far as rotary motor 22R is concerned, and vertical position of head 2 and axial force applied to the cap as far as linear motor 22L is concerned. Such information is supplied by motors 22R, 22L to an analysing system 4 that carries out on such information the processing necessary to detect the start of the threads of the cap and the bottle and to measure the cap application angle for each bottle being capped. More particularly, analysing system 4 is to determine in a calibration phase a function relating the passage of the cap through a predetermined vertical position to the starting positions of the threads and, during normal operation of the capping machine, it will use such a function to determine the corresponding starting positions of the threads from the passage of each cap through the predetermined position. The processing results are then supplied by analysing system 4 to control unit 3 for monitoring the capping quality and carrying out possible interventions that become necessary depending on the monitoring results or generally on the information supplied by analysing system 4.

[0038] It is to be appreciated that the terms "vertical position of the head" and "vertical position of the cap" will be indifferently used hereinafter.

[0039] The mechanical structure of capping machine 1 and heads 2 is not of interest for the invention and is wholly conventional, so that it will not be described in detail. For the sake of clarity of the description, hereinafter reference will be made, when necessary, to a rotary capping machine (so called turret capping machine).

[0040] Referring to Figs. 2 and 3, according to a first embodiment of the invention the thread starting positions are identified based on the evolution of the vertical position of head 2 during capping, more particularly based on the passage of the cap through a reference vertical position selected in the manner specified below. In the flow chart depicted in Fig. 2, step 101 (start) corresponds to the will of performing a working cycle concerning a certain kind of bottles and caps by means of capping machine 1. The start of the normal operations of capping machine 1 is preceded by a calibration or training phase for analysing system 4, during which a number of sequences of capping cycles are executed by using, for each sequence, a different known condition of starting offset or relative angular position of the notches that, on the cap and the bottle, identify the start of the threads, and by setting moreover a reference vertical position identical for all cycles (steps 102, 103). The number of cycles in each sequence and the number of known conditions of starting offset, and hence the number of sequences, will be such as to provide statistically meaningful results. During each cycle, the passage of the cap through the reference position is detected and either the corresponding angular position of the turret, hereinafter referred to as "master position" (step 104), or the instant at which the passage occurs is stored. Such information items are equivalent for a rotary capping machine. A function relating the passage of the cap through the predetermined position to the starting positions of the threads, and hence to their starting offset, is determined from the set of master positions stored (step 105). For instance, such a function may be a regression function of the data collected. At this point, the calibration phase is ended.

[0041] During normal operation of the capping machine, at the instant a cap passes through the predetermined position, the corresponding master position is detected and the starting relative angular position of the threads is determined by using the function determined in the calibration phase (step 106). The normal capping operations then continue until the complete cap tightening (detected in any known manner) and, when this is attained, the angle by which the cap has rotated from the thread start determined at step 106 is measured (step 107). Steps 106, 107 will be repeated for each bottle for the whole duration of the working cycle (step 108). Once the working cycle is over, the method has come to an end (stop, step 109).

[0042] It is to be appreciated that in certain capping machines the nominal application angle is set in advance. In this case "measuring the application angle" means verifying that the complete tightening is attained after a rotation falling in a range including the nominal angle and characterising a good capping.

[0043] Fig. 3 graphically illustrates the principle on which this first embodiment is based and shows how the evolution of the vertical position of a head 2, and hence of the cap, depends on the starting alignment of the threads. Curve families A, B, C, D show, each for a plurality of capping cycles, the evolution of the vertical position of a cap as a function of the angular position of the turret (Master pos.) in an equal number of conditions of starting alignment. Curve E is a reference curve representative of the evolution of the vertical position in theoretical conditions. Dashed line F denotes the reference vertical position that, generally, corresponds to a point of the downward movement of the head where cap screwing has already started and that, as shown in the drawing, is chosen so that the effect of the different starting alignment is readily appreciable.

[0044] Referring to Figs. 4 to 6, a second embodiment of the invention will be described, in which the starting relative angular position of the threads is determined by detecting the vertical position of the point where the first contact between the cap and the bottle occurs. As shown in Fig, 4, such a position depends on the relative angular position of cap 10 and bottle 11, and hence of the respective threads 12, 13, so that the positions of first contact between cap 10 and bottle 11 corresponding to two different relative angular positions of the respective threads 12, 13 will differ by a value A.

[0045] As shown in the flow chart depicted in Fig. 5, after the start (step 201, corresponding to step 101 in Fig. 2), the first step 202 is lowering head 2 as long as it attains the level where the first contact between cap 10 and bottle 11 (and hence between threads 12, 13) occurs. At this level the downward movement is stopped. When such a level is reached, the vertical and angular positions of the head are detected and stored (step 203) and the execution of a sequence of cycles starts, in each of which the head is lifted up to the level of disengagement between cap 10 and bottle 11 and then is brought again to the first contact level with a different relative angular position between cap 10 and bottle 11 (step 204). The evolution of the vertical position of the cap in a number of such cycles is shown in Fig. 6. At each passage through the first contact position, the corresponding vertical and angular positions of the head are detected and stored (step 205). When a statistically meaningful number of detections has been obtained, a function relating the passage of cap 10 through the position of first contact with bottle 11 to the starting positions of threads 12, 13 (step 206) can be determined. In this embodiment too the function may be a regression function. The calibration phase is thus ended.

[0046] The manner in which the cycles are executed, and more particularly the overall variation of the angular positions of the cap and the bottle at the end of the cycle sequence will be chosen also depending on the characteristics of the threads, e.g. depending on whether they are single-start or multi-start threads.

[0047] During normal operation of capping machine 1, the passage of the individual caps through the first contact position is detected (e.g. as the instant or the level at which such passage occurs) and the starting positions of the threads are obtained by using the function determined at the previous step (step 207). As in the first embodiment, the normal capping operations then continue until the complete tightening of cap 10, and the angle by which the cap has rotated from the thread start detected at step 207 is measured (step 208). The operations then go on until the end of that working cycle (steps 209, 210).

[0048] The invention actually solves the problems of the prior art. Indeed, the detection of the starting positions of threads 12, 13 makes use of a function that is determined off line and hence it does not interfere with the duration of the capping operations. Moreover, even if in an embodiment determining that function requires the cap counterrotation up to the level of loss of contact between the threads, the detection of the head fall is not exploited and hence the invention can be applied without problems also in case of tapered threads.

[0049] It is clear that the above description has been given only by way of non-limiting example and that changes and modifications are possible without departing from the scope of the invention as defined in the following claims.

[0050] More particularly, even if analysing system 4 has been shown in Fig. 1 as an element separate from control unit 3, it could also be part of the latter.

[0051] Further, even if with reference to Figs. 4 to 6 the function relating the passage of the cap through the position of first contact between cap 10 and bottle 11 to the starting positions of threads 12, 13 has been determined by executing cycles each including lifting the head up to the position of loss of contact between cap 10 and bottle 11 and bringing it again to the first contact position with a different relative angular position of cap 10 and bottle 11, the same function could be obtained for instance by means of a study of the geometries of threads 12, 13.

[0052] Lastly, in order to detect the starting positions of the threads during normal operation of capping machine 1, instead of using a function relating the passage of the cap through a certain position to said starting positions, analysing system 4 could exploit a neural network allowing extracting from the overall evolution of the vertical position of the cap information about the thread start, contained in said evolution. Hence, by analysing in real time the whole (or part) of the evolution of vertical position p during capping, i.e. a function p(t), and by inputting such a function to a previously trained neural network, the latter can output the thread starting position of the current cycle. Possibly, the network could be integrated by using also other available variables (torque, angular position of the head, master angular position of the turret, time. . .) so as to improve the estimate precision. Moreover, by using such neural networks, the starting alignment can be estimated until few instants before capping is over so as to take corrective actions in the cycle in progress.

Claims

Claims1. Capping method for applying screw caps (10) to containers (11), wherein, during capping, a cap (10) performs a rotary motion about an axis and a vertical translational motion along the same axis, which motions are imparted by respective electrical motors (22R, 22L), and wherein the starting positions of the threads (12, 13) of a cap (10) and a container (11) are detected for monitoring the application angle of the cap (10), the method being characterised in that it includes, for each container (11) being capped, the steps of:- analysing, on the basis of information supplied at least by the motor (22L) imparting the translational motion to the cap (10), the evolution of the vertical position of the cap (10) during at least part of a capping operation and optionally detecting, during the analysis, the passage of the cap (10) through a predetermined position;- determining a function representative of said evolution and optionally a function that relates the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13) and that is obtained in a calibration phase by processing information supplied by the motors (22R, 22L) imparting the rotary and translational motions to the cap;- determining the starting positions of the threads (12, 13) by using either the function representative of the evolution of the vertical position of the cap or the function relating the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13); and- measuring the rotation performed by the cap (10) from the starting positions of the threads (12, 13) thus determined until completion of the capping.

2. Method according to claim 1, wherein the steps of analysing the evolution of the vertical position of the cap (10) and determining the starting positions of the threads (12, 13) by using a function representative of such evolution are performed by means of a neural network to which said function is inputted.

3. Method according to claim 2, wherein said neural network receives, besides the function representative of the evolution of the vertical position of the cap, also information about one or more further parameters characterising the capping operations, which information is supplied also by the motor (22R) imparting the rotary motion to the cap (10).

4. Method according to claim 3, wherein said one or more further parameters are chosen at least among: torque applied to the cap; axial force applied to the cap; position of a capping head (2a...2n) carrying out capping; time.

5. Method according to claim 1, wherein the predetermined position is a position (F)reached by the cap (10) before completion of its tightening on the container (11), and the step of determining said function relating the passage of the cap (10) through the predetermined position (F) to the starting positions of the threads (12, 13) includes detecting the passage of the cap (10) through the predetermined position (F) during the execution of a plurality of sequences of capping cycles, where each sequence is executed with a different starting relative angular position of the threads (12, 13).

6. Method according to claim 5, wherein the step of determining said function relating the passage of the cap (10) through the predetermined position (F) to the starting positions of the threads (12, 13) includes detecting and storing, at each passage of the cap through the predetermined position, the position of the capping head (2a...2n) carrying out capping or the instant at which such a passage occurs.

7. Method according to claim 1, wherein the predetermined position is the position where the first contact between the cap (10) and the container (11) occurs during capping, and the step of determining said function relating the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13) includes detecting the passage of the cap (10) through said first contact position in a plurality of cycles in each of which the cap (10) is lifted from the first contact position up to a position of loss of contact with the container (11) and is brought again to the first contact position with a different relative angular position of the cap (10) and the container (11).

8. Method according to claim 7, wherein the step of determining said function relating the passage of the cap (10) through the predetermined position (F) to the starting positions of the threads (12, 13) includes detecting and storing, at each passage of the cap (10) through the first contact position, the corresponding vertical and angular positions of the cap.

9. Method according to claim 1, wherein the predetermined position is the position where the first contact between the threads (12, 13) of the cap (10) and the container (11) occurs during capping, and the step of determining said function relating the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13) includes analysing the geometries of the threads (12, 13).

10. Method according to any of claims 5 to 9, wherein said function relating the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13) is a regression function of the data collected during the calibration phase.

11. Electronic capping machine (1) for applying screw caps (10) to containers (11), comprising at least one capping head (2a...2n) including electrical motors (22R, 22L) forsimultaneously imparting to a cap, during a capping cycle, a rotary motion about an axis and a vertical translational motion along the same axis, and including processing means (4) for processing information supplied by the motors (22R, 22L), in particular for detecting the starting positions of the threads (12, 13) of the cap (10) and the container (11) for monitoring the application angle of the cap (10), characterised in that the processing means (4) are programmed for:- analysing, on the basis of information supplied at least by the motor (22L) imparting the translational motion to the cap (10), the evolution of the vertical position of the cap (10) during at least part of a capping operation and optionally detecting, during the analysis, the passage of the cap (10) through a predetermined position;- determining a function representative of said evolution and optionally a function that relates the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13) and that is obtained in a calibration phase of the processing means (4) by processing information supplied by the motors (22R, 22L) imparting the rotary and translational motions to the cap;- determining the starting positions of the threads (12, 13) by using either the function representative of the evolution of the vertical position of the cap or the function relating the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13); and- measuring the rotation performed by the cap (10) from the starting positions of the threads (12, 13) thus determined until completion of the capping.

12. Capping machine (1) according to claim 11, wherein the processing means (4) include a neural network to which said function representative of the evolution of the vertical position of the cap (10) is inputted.

13. Capping machine (1) according to claim 12, wherein said neural network receives as input, besides the function representative of the evolution of the vertical position of the cap (10), also information about one or more further parameters characterising the capping operations, which information is supplied also by the motor (22R) imparting the rotary motion to the cap (10), and wherein said one or more further parameters are chosen at least among: torque applied to the cap; axial force applied to the cap; position of the capping head (2a...2n) carrying out capping; time.

14. Capping machine (1) according to claim 11, wherein the predetermined position is a position (F) reached by the cap (10) before completion of its tightening on the container (11), and the processing means (4) are programmed for determining said function relatingthe passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13) by detecting the passage of the cap through the predetermined position in each cycle of a plurality of sequences of capping cycles, where each sequence is executed with a different starting relative angular position of the threads (12, 13).

15. Capping machine (1) according to claim 14, wherein, for determining said function relating the passage of the cap (10) through the predetermined position (F) to the starting positions of the threads (12, 13), the processing means (4) are programmed for detecting and storing, at each passage of the cap (10) through the predetermined position, the position of a capping head (2a...2n) operating on the cap or the instant at which such a passage occurs.

16. Capping machine (1) according to claim 11, wherein the predetermined position is the position where the first contact between a cap (10) and a container (11) occurs, and the processing means (4) are programmed for determining said function relating the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13) by detecting the passage of the cap through the first contact position in each cycle of a plurality of cycles in each of which the cap (10) is lifted from the first contact position up to a position of loss of contact with the container (11) and is brought again to the first contact position with a different relative angular position of the cap (10) and the container (H).

17. Capping machine (1) according to claim 16, wherein, for determining said function relating the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13), the processing means (4) are programmed for detecting and storing, at each passage of the cap (10) through the first contact position, the corresponding vertical and angular positions of the cap.

18. Capping machine (1) according to claim 11, wherein the predetermined position is the position where the first contact between a cap (10) and a container (11) occurs, and the processing means (4) are programmed for determining said function relating the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13) by analysing the geometries of the threads (12, 13).

19. Capping machine (1) according to any of claims 14 to 18, wherein the processing means (4) are programmed for determining said function relating the passage of the cap (10) through the predetermined position to the starting positions of the threads (12, 13) as a regression function of the data collected during the calibration phase.

Images