Method for determining a preform throughput

Abstract

The invention relates to a method for determining the throughput (Qin) of preforms (18) in a supply device (12) for supplying loose preforms (18), which is arranged at the inlet of a facility for the series production of containers by stretch-blow moulding the preforms (18), the supply device (12) comprising a belt conveyor (26A, 26B) which conveys loose preforms (18) to a device (14) for aligning and uprighting the preforms, the method being characterised in that it comprises at least one cycle comprising the following steps: - a first step (E1) of capturing an image of a section (34) of a conveyor belt (30, 36) of the belt conveyor (26A, 26B); - a second step (E2) of automatically counting the preforms (18) present in the captured image; - a third step (E3) of calculating the instantaneous throughput (Qin) in the image capture zone (54).

Description

METHOD FOR DETERMINING A FLOW OF PREFORMS TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a method for determining the flow rate of preforms in a bulk preform feeding device which is arranged at the entrance of a serial container manufacturing installation by stretch-blowing said preforms, the feeding device comprising at least one belt conveyor which transports bulk preforms from a stock of preforms to a preform alignment and straightening device. TECHNICAL BACKGROUND OF THE INVENTION

[0002] There are known facilities for manufacturing containers from thermoplastic materials, particularly polyethylene terephthalate (PET), by forming preforms, notably by blow molding or stretch blow molding. Such a facility makes it possible to produce containers in very large series at very high rates, for example, exceeding 85,000 bottles per hour.

[0003] According to a well-established technique, such containers are produced in two main stages. The first stage involves injection or injection-compression molding of a PET preform. This preform has a roughly tubular body that is closed at one of its axial ends, while the opposite end is open via a neck. The neck, from this injection molding operation onward, has the final shape of the container's neck. Generally, the container neck has a thread or a groove.

[0004] There are facilities in which the preforms, once injected, are directly transmitted to a forming unit, each preform being transported individually.

[0005] However, in many cases, preforms are first manufactured by injection molding and then blow-molded into the final container shape at a second location on a dedicated manufacturing line. This technology allows the blow-molding operation to be carried out as close as possible to the bottling site, while the injection molding operation can be performed anywhere. Indeed, transporting small preforms is relatively easy and inexpensive, whereas transporting blow-molded containers is economically unviable due to their large size.

[0006] In cases where the injection molding station and the forming plant are two completely independent machines, the preforms are generally delivered in bulk. The forming plant therefore has a preform distribution device equipped with a single-line alignment and preform straightening device. The present invention relates to such a device.

[0007] In such a manufacturing facility, the preforms are continuously held individually by various conveying methods, such as grippers or notches. The preforms thus move one after the other along a production path, passing through various processing units, including a heat conditioning unit and a forming unit. The heat conditioning unit heats the preform body to make it malleable, while the forming unit shapes the preform into the final container by stretch blow molding.

[0008] When the preforms are delivered to the manufacturing facility, they are contained in bulk in containers.

[0009] To allow them to be aligned in a line and straightened all in the same orientation, generally so that their axis is vertical and their neck at the top, a straightening and alignment device is used. Such an alignment and straightening device is, for example, a gravity rail such as that described in document EP 1697238 B1 or a centrifuge bowl such as that described in document WO 2016 / 166459 A1.

[0010] In these alignment and straightening systems, it is anticipated that some preforms may become misaligned or incorrectly straightened. In such cases, mechanisms are in place to eject these preforms from the flow and retrieve them so they can be reintegrated into the preform flow at a later date. These preforms are generally referred to as "recycled preforms," ​​and the ratio between the number of recycled preforms and the number of correctly aligned and straightened preforms is called the "recycling rate."

[0011] To convey bulk preforms to the inlet of the alignment and straightening device, belt conveyors with a conveying belt are commonly used. These can be cleated conveyors, in which the belt is inclined to raise the preforms and is equipped with transverse cleats to prevent the preforms from slipping back to their starting point.

[0012] It can also be a smooth belt conveyor, i.e. without cleats, when the slope is low or zero.

[0013] The preforms are poured in bulk onto the conveyor belt by means of a hopper.

[0014] In order for the alignment and straightening device to deliver a regular flow of preforms adapted to the operating rate of the installation, it is necessary to supply it with a sufficient flow of preforms.

[0015] Currently, the preform throughput is estimated based on the conveyor belt speed. However, the actual inflow can fluctuate depending on the belt condition or how the preforms are distributed in the hopper.

[0016] These fluctuations can lead to over-powering of the alignment and rectification device, resulting in untimely blockages and / or increased recycling rate.

[0017] In addition, these fluctuations can also lead to under-powering of the alignment and rectification device, which results in a risk of slowing down the operating rate of the installation.

[0018] Therefore, there is a need to ensure that the alignment and straightening device can properly supply the manufacturing facility while reducing the recycling rate. BRIEF SUMMARY OF THE INVENTION

[0019] The invention proposes a method for determining the flow rate of preforms in a bulk preform feeding device arranged at the inlet of a serial container manufacturing installation by stretch-blowing said preforms, the feeding device comprising at least one belt conveyor which transports bulk preforms from a preform stock to a preform alignment and straightening device,

[0020] characterized in that it comprises at least one cycle including the following steps:

[0021] - a first step of image capture of a section of a conveyor belt by an image capture device in an image capture zone;

[0022] - a second step of automatic counting of the preforms present on said captured image;

[0023] - a third step of calculating the instantaneous flow rate at the image capture area as a function of the conveyor belt speed, the number of preforms counted on the image during the second step and the length of the section visible on the image.

[0024] According to another feature of the invention, the conveyor belt is divided into a fixed number of sections of equal lengths, the image capture device being capable of capturing an image representing the entirety of one of said sections.

[0025] According to another feature of the invention, each image captured during the first step represents a section without overlap with adjacent sections.

[0026] According to another feature of the invention, the cycle is repeated at each successive passage of one of said sections through the image capture area.

[0027] According to another feature of the invention, the repetition frequency of each cycle is proportional to the speed of the conveyor belt.

[0028] According to another feature of the invention, the second automatic counting step is carried out by a shape recognition software which is capable of automatically analyzing the image captured during the first step to recognize each preform and count them.

[0029] According to another feature of the invention, said recognition software implements an image recognition model previously trained by automatic learning.

[0030] According to another feature of the invention, each section of the conveyor belt is associated with a unique identification reference, the number of preforms counted on each section being stored by an electronic control unit in association with its unique identification reference and in association with a unique cycle number.

[0031] According to another feature of the invention, the conveyor belt is inclined to raise preforms above the alignment and straightening device.

[0032] According to another feature of the invention, the conveyor belt includes cleats, each section of the belt being physically delimited by two cleats. BRIEF DESCRIPTION OF THE FIGURES

[0033] Other features and advantages of the invention will become apparent during the reading of the detailed description which follows, for the understanding of which reference should be made to the attached drawings briefly described below.

[0034] This is a perspective view which represents a preform distribution device and an associated feeding device for the implementation of the process according to the teachings of the invention.

[0035] Laest is a front view which represents a preform adapted for use with the device of the, the axis of the preform being here oriented vertically.

[0036] This is a schematic side view representing a conveyor belt of a first inclined inlet conveyor of the feeding device which is equipped with cleats.

[0037] This is a schematic side view that represents a horizontal conveyor belt of a second infeed conveyor of the feeding device which is smooth.

[0038] This is a perspective view from above of the conveyor belt of the second infeed conveyor which is equipped with preform counting means.

[0039] This is a block diagram that represents the process of determining the flow rate of preforms on the second infeed conveyor. DETAILED DESCRIPTION OF THE FIGURES

[0040] In the following description, elements with an identical structure or analogous functions will be designated by the same references.

[0041] A schematic representation of a preform distribution device 10 is shown, which includes:

[0042] - a device 12 for feeding bulk preforms;

[0043] - a preform straightening and alignment device 14 which is supplied with preform by the feeding device 12;

[0044] - an output conveyor 16 which receives preforms aligned in a line and straightened by the straightening and alignment device 14.

[0045] An example of a preform 18 intended for use with the straightening and alignment device 14 is illustrated in Figure 1. Such a preform 18 is made of thermoplastic material, here polyethylene terephthalate (PET). It is conventionally obtained by injection molding. It has a substantially axisymmetric shape around a principal axis "A" shown vertically in Figure 1.

[0046] It comprises a body 20 in the shape of an elongated tube along the main axis "A" having a closed axial end and which has at its opposite end, shown at the top, an axially open neck 22.

[0047] The preform 18 also includes an annular support face 24 which is oriented axially towards the closed end of the preform 18, which protrudes radially from the rest of the body 20. The support face 24 is arranged above a center "G" of gravity of the preform 18. The support face 24 goes around the preform 18 either continuously, as illustrated in the figure, or discontinuously (not shown).

[0048] In the example shown in the figure, the base of the neck 22, at the junction with the body 20, has a collar which extends radially in projection relative to the rest of the preform 18. The lower face of the collar thus forms said support face 24.

[0049] As an alternative not shown, the collar can be arranged elsewhere than at the base of the neck, for example at the level of the mouth.

[0050] According to another variant not shown, the support face 24 is for example formed by a lower face of a thread of the neck.

[0051] According to yet another variant not shown, the support face 24 is attached to the preform 18, for example by means of a plug.

[0052] An external diameter "D1" of the support face 24, in this case the collar, is thus greater than the maximum external diameter "D2" of the body 20, located here directly under the collar.

[0053] Neck 22 has its final shape, while body 20 is intended to be stretched in a subsequent forming operation to form the body of the finished container.

[0054] The example shown is not limiting. It will be understood that the distribution device 10 is intended to support any type of preform 18 having a support face 24 that protrudes radially from the rest of the body 20, and having a center of gravity that is axially offset towards the body 20 with respect to said support face 24.

[0055] As will be explained later, the distribution device 10 is capable of processing identical batches of preforms 18, although the format of the preforms 18 may vary from batch to batch. Therefore, different adjustments may be required on the various components of the distribution device 10 when the format of the preform 18 changes.

[0056] As shown in Figure 1, the feeding device 12 includes at least one belt conveyor 26A, 26B, each of which has a conveyor belt that travels at a predetermined speed "V". Each conveyor belt transports the bulk preforms 18 from a hopper 29 to the straightening and alignment device 14. The hopper 29 contains a stock of bulk preforms.

[0057] The speed "V" of the conveyor belts is, for example, controlled according to the input flow rate "Qin" required for proper operation of the manufacturing installation.

[0058] By way of non-limiting example, and as shown in Figure 1, a first belt conveyor 26A includes a cleated conveyor belt 30 at the lower end of which preforms 18 are discharged in bulk from the hopper 29. The cleated conveyor belt 30 of the first belt conveyor 26A is inclined to raise the preforms 18, as indicated by arrow F1 in Figure 1. It includes transverse cleats 32 that divide the cleated conveyor belt 30 into several sections 34 of identical dimensions. The cleats 32 prevent the preforms 18 from sliding down the cleated conveyor belt 30.

[0059] The feeding device 12 here includes, in addition to the first belt conveyor 26A, a second belt conveyor 26B comprising a horizontal conveying belt 36 which allows the preforms 18 to be conveyed in bulk from the upper end of the first belt conveyor 26A to a feeder discharge point of the straightening and alignment device 14, in the direction of arrow F2 of the.

[0060] For each conveyor belt 30, 36, the useful length is defined as the length of the strand that actually carries the preforms 18, the return strand to the entrance of the belt conveyor 26A, 26B is not taken into account.

[0061] As explained in the introduction, it is important to know precisely the flow rate of preforms 18 conveyed by the feeding device 12 at any given time to guarantee a regular flow of preforms 18 adapted to the operating rate of the manufacturing installation. The invention therefore proposes a method for determining the flow rate "Qin" of preforms in the feeding device 12.

[0062] To determine the input flow rate "Qin" of preforms 18, the feeding device 12 is equipped with means for counting the preforms 18. The input flow rate "Qin" is calculated based on the quantity of preforms 18 counted per unit of time.

[0063] As shown in Figure 1, the means for counting the preforms 18 include an image-capturing device 52, such as a camera capable of capturing an image in a digital format readable by an electronic control unit 53, such as a computer. The image-capturing device 52 is fixedly mounted relative to the ground. It is capable of capturing images of successive sections 34 of the conveyor belt 30, 36 of one of the belt conveyors 26A, 26B.

[0064] In the example of the image capture device 52, it is associated with the second conveyor belt 26B.

[0065] In an unrepresented variant of the invention, the image capture device 52 is associated with the first belt conveyor 26A.

[0066] The image capture device 52 is capable of capturing an image of an image capture zone 54 that is fixed relative to the ground. The image capture zone 54 is much smaller than the usable length of the conveyor belt 36, so that only the image of a section 34 of the conveyor belt 36 can be captured at any given time. Thus, as the conveyor belt 36 moves, its entire length passes successively through the image capture zone 54.

[0067] As shown in Figure 1, the method for determining the "Qin" flow rate of preforms 18 comprises at least one cycle consisting successively and in order of the following steps:

[0068] - a first step "E1" of image capture of a section 34 of the conveyor belt by the image capture device 52 in the image capture zone 54;

[0069] - a second step “E2” of automatic counting of the 18 preforms present on said captured image;

[0070] - a third step "E3" of calculation of the instantaneous flow rate "Qin" at the level of the image capture zone 54 as a function of the speed "V" of the conveyor belt 36, the number of preforms 18 counted on the image and the length of the section 34 visible on the image.

[0071] The image capture frequency is configured so that the portions of conveyor belt 29 captured in successive images are directly adjacent, to ensure no preforms 18 are missed, and without overlapping, to prevent the same preforms 18 from appearing in two images. Thus, the image capture frequency depends on the speed "V" of the conveyor belt 29 from the infeed conveyor 26B.

[0072] These images are then sent to an electronic control unit 56 which is capable of recognizing the preforms 18, for example by means of pattern recognition software, and of automatically counting the quantity of preforms 18 recognized on each image.

[0073] Then, the electronic control unit 56 automatically calculates the instantaneous flow rate of preforms 18 at the image capture zone 54 based on the speed "V" of the conveyor belt 29 of the infeed conveyor 26B, the quantity of preforms 18 counted in the image, and the length of the visible section in the image. This instantaneous flow rate constitutes the infeed flow rate "Qin" of preforms 18.

[0074] The second step "E2" of automatic counting is carried out by the electronic control unit 56 using shape recognition software which is capable of automatically analyzing the captured image to recognize each preform 18 and counting them.

[0075] The said recognition software can implement a pre-trained image recognition model using machine learning to recognize different preform patterns in different positions.

[0076] During the third calculation step "E3", the instantaneous flow rate "Qin" of preforms 18 is calculated, for example, according to the following formula:

[0077]

[0078] in which: “Qin” is the instantaneous flow rate of preforms 18 when the section 34 passes through the capture zone 54; “N” is the number of preforms counted on the image captured during the second automatic counting stage “E2”; “L” is the length of the section 34 taken in the direction of travel of the conveyor belt 36.

[0079] The conveyor belt 36 is divided into a fixed number of sections 34 of equal length. The image capture device 52 is capable of capturing an image representing the entirety of one of these sections 34 when it passes through the capture zone 54.

[0080] With regard to the second conveyor 26B with belt, the conveyor belt 36 is divided into sections 34 which are physically delimited according to the position of the conveyor belt 36 determined by the electronic control unit 53 for example according to the operation of the conveyor belt drive motors.

[0081] Alternatively, when the process is applied to the first belt conveyor 26A, each section 34 is advantageously physically delimited by two successive cleats 32.

[0082] Each captured image represents a 34-section without overlap with adjacent 34-sections, thus there is no risk of counting the same preforms twice 18.

[0083] In addition, the 34 segments are all directly adjacent to each other and an image of each of the 34 segments is successively taken as it passes through the capture zone 54.

[0084] The cycle is repeated at each successive passage of one of said sections 34 through the image capture zone 54.

[0085] Thus, there is no "dead" section of the conveyor belt 36 whose image would not be captured by the image capture device 52.

[0086] To capture an image of each section 34, the repetition frequency of each cycle is proportional to the speed "V" of the conveyor belt 26B. Thus, the higher the speed "V", the higher the repetition frequency of each cycle.

[0087] Advantageously, each section 34 of the conveyor belt 36 is associated with a unique identification reference by the electronic control unit 53. Thus, the number "N" of preforms 18 counted on each section 34 is stored by the electronic control unit 53 in association with its unique identification reference and in association with a unique cycle number.

[0088] This makes it possible in particular to determine whether a particular section 34 of the conveyor belt 36 is problematic or whether there are regular fluctuations which would indicate a malfunction, for example a defect at the level of a cleat 32 or a defect at the level of the hopper 29.

[0089] The invention thus makes it possible to determine with great precision the flow rate of preforms passing through the feeding device 12 at any given time. This allows, in particular, the speed "V" of the conveyor belts 30, 36 to be adjusted according to fluctuations in the flow rate "Qin", but also to detect any problems with the feeding of the preforms 18.

Claims

A method for determining the flow rate (Qin) of preforms (18) in a bulk preform (18) feeding device (12) arranged at the inlet of a container manufacturing installation by stretch-blowing said preforms (18), the feeding device (12) comprising at least one belt conveyor (26A, 26B) that transports bulk preforms (18) from a preform stockpile (18) to a preform alignment and straightening device (14), characterized in that it comprises at least one cycle including the following steps: - a first step (E1) of capturing an image of a section (34) of a conveyor belt (30, 36) of the belt conveyor (26A, 26B) by an image-capturing device (52) in an image-capturing zone (54); - a second step (E2) automatic counting of preforms (18) present on said captured image;- a third step (E3) of calculating the instantaneous flow rate (Qin) at the level of the image capture zone (54) as a function of the speed (V) of the conveyor belt (30, 36), the number (N) of preforms (18) counted on the image during the second step (E2) and the length (l) of the section (34) visible on the image.; Method according to the preceding claim, characterized in that the conveyor belt (30, 36) is divided into a fixed number of sections (34) of equal lengths, the image capture device (52) being capable of capturing an image representing the entirety of one of said sections (34). A method according to the preceding claim, characterized in that each image captured during the first step (E1) represents a section (34) without overlap with the adjacent sections (34). Method according to any one of claims 2 or 3, characterized in that the cycle is repeated at each successive passage of one of said sections (34) in the image capture zone (54). Method according to the preceding claim, characterized in that the repetition frequency of each cycle is proportional to the speed (V) of the conveyor belt (30, 36). Method according to any one of claims 2 to 5, characterized in that the second step (E2) of automatic counting is carried out by a shape recognition software which is capable of automatically analyzing the image captured during the first step (E1) to recognize each preform (18) and count them. Method according to the preceding claim, characterized in that said recognition software implements an image recognition model previously trained by automatic learning. A method according to any one of the preceding claims, characterized in that each section (34) of the conveyor belt (30, 36) is associated with a unique identification reference, the number (N) of preforms (18) counted on each section (34) being stored by an electronic control unit (56) in association with its unique identification reference and in association with a unique cycle number. A method according to any one of the preceding claims, characterized in that the conveyor belt (30) of the conveyor (26A) is inclined to raise preforms (18) above the alignment and straightening device (14). Method according to the preceding claim taken in combination with claim 2, characterized in that the conveyor belt (30) comprises cleats (32), each section (34) of belt being physically delimited by two cleats (32).

Images