Method for determining thrust generated by cumulative conveyor

Abstract

The invention relates to a method of determining a thrust force (F) generated by an accumulation conveyor (22) against preforms (14) of containers, said accumulation conveyor (22) comprising:-a pair of support rails (34) of the preforms (14); -at least one endless flexible element (42) comprising a friction element (44) that rubs against said preform (14); -means for driving the endless flexible element (42), comprising a motor (54) which transmits a motor torque (Cm) to the endless flexible element (42); characterized in that it comprises: a first step (E1) of determining the motor torque (Cm) provided to the endless flexible element (42); a second step (E2) of estimating the thrust (F) from the motor torque (Cm) determined in the first step (E1).

Description

Technical Field

[0001] The present invention relates to a method for determining the thrust exerted by an accumulation conveyor on preforms, in particular preforms made of thermoplastic material, each preform having a flange, the accumulation conveyor comprising: - a pair of support rails that support the preforms by means of the flanges of the preforms, the support rails being adapted to guide the preforms along a path;

[0002] - at least one endless flexible element, the endless flexible element comprising a friction element that rubs against the preform, a tension strip of the endless flexible element being arranged along the path, and the friction element driving the strip generates a thrust along the path of the preform by rubbing against the preform;

[0003] - a drive device for the endless flexible element, including a motor that transmits a motor torque to the endless flexible element. Background Art

[0004] Preform accumulation conveyors are intended to be used in manufacturing equipment for containers made of thermoplastic material (in particular polyethylene terephthalate (PET)), the equipment manufacturing the containers by forming the preforms (in particular by blow molding or stretch blow molding). Such manufacturing equipment allows the mass production of containers at very high speeds, for example more than 85,000 bottles per hour.

[0005] According to a well-known technique, the production of such containers is mainly divided into two steps.

[0006] In the first step, preforms made of PET are manufactured by injection molding. The preform has a substantially tubular body, one of the axial ends of the body being closed and the other end being open through a neck. During the injection molding operation, the neck already presents the final shape of the container neck. Usually, the neck of the container has a thread.

[0007] In the second forming step, the hot preform is placed in a mold cavity. Then, a pressurized forming fluid is injected into the preform so that the wall of the preform adheres to the wall of the mold cavity, thereby forming the preform into the final container. This blow molding operation is usually accompanied by a stretching operation, i.e., by inserting a stretching rod into the preform to stretch its body in order to axially stretch the wall of the preform.

[0008] Typically, the preforms are manufactured by injection molding in a first location and then blow molded into the final shape of the container on a specific manufacturing device in a second location. This technique allows the blow molding operation to be carried out as close as possible to the bottling site, while the injection molding operation can be carried out anywhere. In fact, it is relatively easy and inexpensive to transport the smaller-sized preforms, while transporting the blow-molded containers has the disadvantage of being economically unfeasible because of their very large volume.

[0009] In the case where the injection molding station and the forming manufacturing equipment are two completely independent machines, the preforms are usually delivered in bulk. Therefore, the manufacturing equipment is equipped with means for aligning the preforms in a single row and standing them upright. Such manufacturing equipment also includes at least one heating station and a blow molding station for blow molding containers from the hot preforms.

[0010] The present invention particularly relates to a preform aligning and standing device in which the preforms are not indexed in position. However, most of the time, the preforms are output in the form of strings of closely arranged preforms, with each preform in contact with the next.

[0011] From the inlet of the heating station to the outlet of the forming station, the preforms are picked up one by one by gripping means such as a turntable or clips. Thus, the preforms move in a single row one by one along the production path.

[0012] The start of the forming cycle for producing containers at a rate of tens of thousands of pieces per hour does not depend on the presence of preforms in the relevant mold. Therefore, in the case where one or more preforms are missing from the preform stream, the forming unit rotates and the mold that would originally accommodate these preforms is empty. This results in a waste of energy and a reduction in productivity.

[0013] However, the preforms may not be in contact with each other when leaving the aligning and standing device. This creates a gap between two strings of preforms, which may interfere with the feeding at subsequent workstations. Therefore, there will be empty spaces on the subsequent conveyor. The efficiency of the manufacturing equipment may be reduced.

[0014] To avoid this phenomenon, it is known to provide an accumulation conveyor between the aligning and standing device and the first processing station of the preforms. Such an accumulation conveyor can accumulate the preforms into an accumulation column, and the preforms are distributed one by one to the next workstation, for example, to a grooved wheel. By distributing the preforms stored in the accumulation column, such an accumulation column leaves time to fill the possible gaps between the strings of preforms leaving the aligning and standing device. The length of the accumulation column is temporarily shortened until the string of preforms that arrives late.

[0015] The accumulation column should contain the minimum number of preforms suitable for the production speed of the container manufacturing equipment to avoid the accumulation column being emptied too quickly during a temporary blockage.

[0016] In order to distribute the preforms in the accumulation column to the next work station, a retractable stop finger is provided, for example, at the end of the accumulation conveyor. It is controlled between a position where it stops the preforms from sliding and a retracted position where it releases the preforms to slide, so as to distribute the preforms to the next conveyor at a determined speed, such that each position of the next conveyor is loaded with a relevant preform. Thus, the preforms waiting in the accumulation column move at a distribution speed corresponding to the said speed.

[0017] In order to be able to fill the gaps between the strings of preforms, the accumulation conveyor advantageously allows the preforms to be advanced into the accumulation column at a free movement speed higher than the distribution speed of the accumulation column. For example, the length of the accumulation column is adjusted by controlling the conveying amount of the arranging and uprighting device.

[0018] Such an accumulation conveyor mainly includes a slide rail defined by two support guide rails. The preforms are supported on the support guide rails by their flanges, and the bodies of the preforms hang between the support guide rails. Devices are also provided for driving all the preforms along the entire length of the accumulation conveyor. In fact, without such driving devices, the preforms passively pushed by the pressure of the preforms upstream of the accumulation column may get stuck between the guide rails, resulting in blockages.

[0019] It is known to use a so-called "brush conveyor" as the accumulation conveyor, which can greatly reduce the vertical space occupied compared with a gravity rail conveyor.

[0020] This brush conveyor includes guide rails, and the preforms are slidably received between the guide rails. An endless belt equipped with friction elements (here brushes) is arranged on both sides of the path of the preforms. Thus, the body of the preform is surrounded by the tensioned strips of each belt along the path of the guide rails. The friction elements (here the bristles of the brushes) rub against the body of the preform and push it towards the downstream end of the guide rail outlet with a determined thrust. In this way, a preform is quickly pushed by the brushes towards the downstream end of the outlet until it reaches the accumulation column.

[0021] When the preform reaches the accumulation column, it always moves more slowly towards the downstream end of the accumulation column under the frictional force of the bristles at the distribution speed. The brushes usually move faster than the preforms in the accumulation column. The flexibility of the bristles can prevent belt blockages or preform damage.

[0022] In order to make the thrust in the optimal working range, it is very important to adjust certain structural parameters and operating parameters.

[0023] In fact, if the thrust is too high, for example, violent collisions may occur between the preforms, resulting in their damage. This may also lead to premature wear of the strip friction elements. Therefore, if the thrust is too large, it needs to be detected as early as possible in order to reduce the production speed of the manufacturing equipment and reduce the risk.

[0024] Conversely, if the thrust is insufficient, the preforms may not be effectively grasped by the subsequent conveyor, for example, resulting in empty spaces on the subsequent conveyor, as mentioned above.

[0025] Among the structural parameters to be controlled, the lateral spacing between the drive belts of the strip is mentioned as an example, which must be adapted to the diameter of the preform, and also the tension of the strip. Among the operating parameters, the rotational speed of the strip can be mentioned as an example.

[0026] So far, the method for controlling the thrust is to interrupt production in order to insert a test preform connected to a dynamometer into the accumulation conveyor, so as to directly measure the thrust. This means that certain components of the accumulation conveyor need to be regularly disassembled in order to insert the dynamometer. This operation is highly restrictive and is usually carried out when the size of the preforms processed by the manufacturing equipment changes.

[0027] In addition, this method cannot track the thrust changes that may occur during operation, because many parameters have an impact, such as the aging of the friction elements, the slack of the strip, and the characteristics of the preforms being processed. Summary of the Invention

[0028] The present invention proposes a method for determining the thrust generated by an accumulation conveyor on preforms, especially those made of thermoplastic materials, each preform having a flange, and the accumulation conveyor includes:

[0029] A pair of support rails for supporting the preform through the flange of the preform, the support rails being used to guide the preform along a path;

[0030] At least one endless flexible element, including a friction element that frictions against the preform, and the tension belt of the endless flexible element is arranged along the path, and the friction element of the drive belt generates a thrust along the path of the preform by frictione against the preform;

[0031] A drive device for the endless flexible element, including a motor, the motor transmitting a motor torque to the endless flexible element. The method according to the present invention is characterized in that the method includes:

[0032] A first step of determining the motor torque provided to the endless flexible element;

[0033] A second step of estimating the thrust based on the motor torque determined in the first step.

[0034] Another feature of the method implemented according to the teachings of the present invention is that the thrust is also estimated based on the rotational speed of the endless flexible element.

[0035] Another feature of the method implemented according to the teachings of the present invention is that the motor is an electric motor, and the motor torque is determined based on the electric power supplied to the electric motor and the rotational speed of the endless flexible element.

[0036] Another feature of the method implemented according to the teachings of the present invention is that the power supply to the electric motor is controlled by an electronic speed controller, the rotational speed of the endless flexible element is an input set value, and the motor torque is the output value of the electronic speed controller.

[0037] Another feature of the method implemented according to the teachings of the present invention is that the motor torque is determined by measurement using an external torque measuring device placed between the motor and the endless flexible element.

[0038] Another feature of the method implemented according to the teachings of the present invention is that the thrust is calculated based on the value of the motor torque measured over a determination period.

[0039] Another feature of the method implemented according to the teachings of the present invention is that the correlation between the thrust and the motor torque is determined experimentally.

[0040] Another feature of the method implemented according to the teachings of the present invention is that when the thrust determined in the second step shows an excessive deviation from the reference thrust, an alarm signal is issued.

[0041] Another feature of the method implemented according to the teachings of the present invention is that when the alarm signal is issued, the motor is controlled to change the set speed of the endless flexible element to achieve the required thrust.

[0042] Another feature of the method implemented according to the teachings of the present invention is that the cumulative conveyor includes two endless flexible elements, and the tension strips of the endless flexible elements are arranged on both sides of the path at a determined lateral spacing; and when the alarm signal is issued, the lateral spacing between the two tension strips is checked to verify whether the spacing is well adapted to the size of the preform to be processed.

[0043] Another feature of the method implemented according to the teachings of the present invention is that when the alarm signal is issued, the position of the guiding element of the preform, such as a guide rail, is checked. Description of the Drawings

[0044] During the process of reading the following detailed description, other features and advantages of the present invention will become apparent. For better understanding, reference may be made to the accompanying drawings briefly described below.

[0045] Figure 1 is a top view, which schematically shows an accumulation conveyor capable of implementing the method according to the teachings of the present invention.

[0046] Figure 2 is a side view, which shows the preforms intended to be handled by the accumulation conveyor in Figure 1 the accumulation conveyor.

[0047] Figure 3 is Figure 1 a vertical cross-sectional view of the preforms conveyed in the accumulation conveyor in

[0048] Figure 4 is a perspective view, which shows in detail the drive wheel of the accumulation conveyor in Figure 1 the accumulation conveyor, which is driven to rotate by a controlled electric motor.

[0049] Figure 5 is a flow chart, which shows the method for determining the thrust applied by the accumulation conveyor in Figure 1 the accumulation conveyor to the preforms conveyed thereby, and the method is implemented according to the teachings of the present invention. DETAILED DESCRIPTION

[0050] In the following description, elements having the same structure or similar functions will be denoted by the same reference numerals.

[0051] In the following description, the conveyance of the preforms 14 in the manufacturing apparatus 10 is carried out from upstream to downstream.

[0052] In the following description, for each preform in the accumulation conveyor implemented according to the teachings of the present invention, the following non-limiting local directions will be adopted:

[0053] — Longitudinal "L", pointing from upstream to downstream along the moving direction of the preform;

[0054] — Transverse "T", orthogonal to the longitudinal "L" and extending in the plane of the guide rails;

[0055] — Vertical direction "V", pointing from bottom to top along the direction opposite to the earth's gravity.

[0056] Figure 1Schematically shows a part of a manufacturing apparatus 10 for manufacturing a container made of a thermoplastic material by molding, in particular by blow molding or stretch blow molding. The manufacturing apparatus 10 here includes an arrangement and an uprighting device 12 for the preforms 14, which are used to supply a heating station 16. The heating station 16 includes a transfer wheel 18, which includes receiving elements for individually receiving each preform 14. Here, the receiving elements are formed by grooves 20 distributed on the periphery of the transfer wheel 18.

[0057] At least one accumulation conveyor 22 is provided between the outlet of the arrangement and uprighting device 12 and the transfer wheel 18 of the heating station 16.

[0058] Figure 2 Shows an example of a preform 14 intended to be used with the arrangement and uprighting device 12. Such a preform 14 is made of a thermoplastic material, here PET. It is usually obtained by injection molding. It is substantially axially symmetric about the Figure 2 vertically represented main axis "A".

[0059] It includes an elongate tubular body 24 along the main axis "A", the body having an axially closed end and the body having an axially upwardly opening neck 26 at the other end ( Figure 2 shown as the upper end in the figure).

[0060] The preform 14 further includes an annular support flange 28, which projects radially relative to the rest of the body 24. The term "annular" means that the flange 28 surrounds the preform 14 and can be continuous or discontinuous. In the latter case, the annular surface is formed, for example, by discontinuous segments around the preform 14, which are close enough so that the preform 14 can be supported by two opposing radial supports regardless of the position of the preform 14 about its main axis "A".

[0061] In the example shown, the annular support flange 28 is provided at the bottom of the neck 26, at the connection with the body 24. Thus, the lower surface of the annular support flange 28 forms a support surface for transporting the preform 14 in a packaging production line.

[0062] As a variant, the annular support flange can be provided at other positions than the bottom of the neck, for example at the bottle mouth.

[0063] Here, the annular support flange 28 is integrally formed with the preform 14, but as a variant, the annular support flange 28 can also be mounted on the preform by, for example, a plug.

[0064] The outer diameter "D1" of the annular support flange 28 is greater than the outer diameter "D2" of the body 24, which is hereinafter referred to as the "diameter D2 below the neck", directly below the annular support flange.

[0065] The neck 26 has its final shape, while the body 24 of the preform 14 will be stretched during subsequent forming operations to form the body of the final container. To this end, the manufacturing device 10 is equipped with a heating station 16, which is arranged downstream of the aligning and erecting device 12, as Figure 1 shown.

[0066] In addition, the weight of the body 24 of the preform 14 used is greater than the weight of the neck 26 (including the weight of the annular support flange 28). Therefore, as Figure 2 shown, the center of gravity "G" of the preform 14 is located below the annular support flange 28. Therefore, the preform 14 supported on two opposite radial support members by the annular support flange 28 is oriented with the neck 26 upward under the action of gravity.

[0067] Figure 2 The example shown is not restrictive. It should be understood that the present invention is intended to be applied to any type of preform 14 that has an annular support flange 28 protruding radially with respect to the rest of the body 24 and whose center of gravity is axially biased towards the body 24 with respect to the annular support flange 28.

[0068] Generally, the preforms 14 are conveyed to the inlet of the aligning and erecting device 12 in bulk form and then arranged and erected and output in a single row through the outlet 30. Here, by way of non-limiting example, this is an aligning and erecting device 12 as described in document WO2016 / 166446A1.

[0069] Due to the possibility of blockages occurring in various types of aligning and erecting devices, the preforms 14 do not leave the aligning and erecting device 12 in a constant manner. Therefore, the output column of preforms 14 may have "gaps" at certain positions, separating two strings of preforms 14, which are the positions where the preforms 14 are temporarily blocked. However, the heating station 16 requires a stable and continuous supply of preforms 14. Therefore, it is not possible to directly supply the heating station 16. Therefore, it is necessary to temporarily stack the preforms 14 in the accumulation column 32 to allow the transfer wheel 18 of the subsequent processing station (here the heating station 16) to be continuously and stably supplied, so as to ensure that each groove 20 of the transfer wheel 18 receives a relevant preform 14.

[0070] Therefore, the accumulation conveyor 22 is arranged between the outlet 30 of the aligning and erecting device 12 and the heating station 16.

[0071] As Figure 3 shown in more detail, the accumulation conveyor 22 includes a slide rail, which includes grooves defined by a pair of support guide rails 34. Here, the support guide rails 34 are straight.

[0072] Each preform 14 is intended to be received in a suspended manner between two support rails 34 so as to guide the sliding of the preform along a rectilinear path 36 as Figure 1 shown. Referring again to Figure 3 , the body 24 of each preform 14 is received in a suspended manner between the support rails 34, and the annular support flange 28 is placed in a sliding manner on the support rails. Each slide rail has an upstream end 38 and a downstream end 40.

[0073] The spacing between the support rails 34 is adjusted to be slightly larger than the diameter D2 below the neck of the preform 14, but smaller than the outer diameter D1 of the annular support flange 28. Therefore, the lateral clearance between the support rails 34 and the body 24 of the preform 14 is sufficient to allow the preform 14 to slide without jamming, while being small enough to prevent the annular support flange 28 from passing through and the preform 14 from falling.

[0074] Non - restrictively, the spacing between the two support rails 34 is adjustable to allow the accumulation conveyor 22 to accommodate preforms 14 of different sizes.

[0075] The accumulation conveyor 22 preferably includes a neck guide 35 that extends directly above the support rails 34 and is at a distance greater than or equal to the height of the neck 26 of the preform 14 from the support rails 34, that is, there is a clearance between the neck guide 35 and the upper end of the preform 14. The function of the neck guide 35 is to prevent the preform 14 from lifting and the annular support flanges 28 of the preforms 14 from overlapping each other. In the example shown, the neck guide 35 is in the shape of a rod with a rectangular cross - section, and its lower plane is a few tenths of a millimeter (at most 1 to 2 millimeters) away from the preform 14.

[0076] The accumulation conveyor 22 also includes drive means for driving the preform 14 towards the downstream end 40 of the path 36. These drive means are designed to directly provide a thrust "F" for each preform 14 over the entire length of the path 36. For example, the thrust "F" is about 5 Newtons.

[0077] Referring again to Figure 1 and Figure 3 , the drive means for the preform 14 includes at least one endless flexible element 42 that carries friction elements 44 on its outer surface, and these friction elements are capable of contacting the preform 14 suspended between the support rails 34 to drive the preform from upstream to downstream along the slide rail by friction. Therefore, the friction elements 44 generate a thrust "F" on each preform 14 by friction. Here, each endless flexible element 42 is constituted by a timing belt.

[0078] As a variant, each endless flexible element is constituted by a single strip or a roller chain.

[0079] Each endless flexible element 42 is tensioned around at least two wheels 46A, 46B having vertical axes Z1, Z2. Here, each endless flexible element 42 is disposed around two wheels 46A, 46B.

[0080] At least one of the wheels forms a drive wheel 46A which transmits the torque "Cm" of the motor to the endless flexible element 42 to drive its rotation, which will be explained in more detail later. The other of the two wheels is here a driven wheel 46B which rotates freely.

[0081] In a variant (not shown) of the invention, both wheels 46A, 46B are drive wheels.

[0082] The endless flexible element 42 has a tensioning strip 48 which is arranged parallel and close to the path 36 of the preform 14 received between the two guide rails 34.

[0083] Here, the accumulation conveyor 22 includes two endless flexible elements 42, where each tensioning strip 48 is arranged transversely opposite on both sides of the path 36 of the preform 14, parallel to the support guide rails 34. Thus, the forces exerted by the friction elements 44 of the two endless flexible elements 42 on each preform 14 are balanced, which enables better driving of the preform 14 when it slides downstream.

[0084] The accumulation conveyor 22 described here is a "brush type" conveyor, where the friction elements 44 are constituted by brushes protruding and extending from the outer surface. In the example shown, each brush includes a row of overlapping tufts of bristles. An example of such a brush type accumulation conveyor 22 is described in detail in the document FR3.028.254A1, and for more details, reference can be made to this document.

[0085] As a variant, the friction elements are constituted by layers of material with a high coefficient of friction, such as leather or silicone, which form the outer surface of the endless flexible element 42.

[0086] The friction elements 44 are particularly used to contact the body 24 of the preform 14. For this purpose, the friction elements 44 (here the bristles) on the tensioning strip 48 of each endless flexible element 42 protrude from below one of the associated support guide rails 34.

[0087] In a variant (not shown), at least part of the friction elements protrude above the support guide rail so as to frictionally abut against the neck of the preform.

[0088] In the example shown in the drawings, the endless flexible element 42 is preferably positioned such that the ends of the bristles of each brush of the tensioning strip 48 (constituting the friction element 44) can extend into the space swept by the body 24 of the preform 14 moving along the support guide 34 from upstream to downstream. Due to the flexibility of the bristles, when contacting the body 24 of the preform 14, the bristles will bend, putting the bristles in a tensioned state, thereby transmitting a force to the preform 14, tending to drive the preform 14 to move.

[0089] Each drive wheel 46A is driven to rotate such that the tensioning strip 48 of the associated endless flexible element 42 moves from upstream to downstream.

[0090] Each endless flexible element 42 is driven to move at a determined set speed "V" by the rotation of the drive wheel 46A. The moving speed "V" of each endless flexible element 42 is controlled by the electronic control unit 50, which is an automatic control here. Figure 4 The control unit is schematically shown therein. The moving speeds "V" of the two endless flexible elements 42 of the cumulative conveyor 22 are synchronized. Therefore, hereinafter, the speed "V" at which the tensioning strip 48 of each endless flexible element 42 moves will be referred to as the "moving speed 'V' of the cumulative conveyor 22".

[0091] As Figure 4 shown, in order to enable each endless flexible element 42 to be driven without slipping, at least the associated drive wheel 46A is provided with a toothed structure 52 on its rim, which meshes with the corresponding groove on the inner surface of the associated endless flexible element 42.

[0092] Each endless flexible element 42 is driven by a drive device including an electric motor 54.

[0093] More specifically, here each drive wheel 46A is driven by the associated electric motor 54, and the electric motor 54 provides a motor torque "Cm". The electric motor 54 is connected to the drive wheel 46A through a transmission. The transmission includes, for example: a shaft 56 with an axis Z1, on which the drive wheel 46A is fixed; and a gear transmission mechanism 58.

[0094] The gear transmission mechanism 58 may include an angular commutator, for example implemented by bevel gears. The gear transmission mechanism 58 can (when needed but not necessarily) change the speed ratio between the electric motor 54 and the drive wheel 46A.

[0095] Here, the electric motor 54 is powered by an electronic speed governor 60 which is connected to the electronic control unit 50 so as to be able to vary the speed “V” of the accumulation conveyor 22. Thus, the electronic control unit 50 sends the reference speed as an input parameter to the electronic speed governor 60 which can then supply the electric motor 54 appropriately to obtain the set speed “V”.

[0096] As long as the preforms 14 are not blocked from moving downstream, the movement of the endless flexible element 42 causes the preforms 14 to advance by friction with the friction element 44. When the preforms 14 reach the end of the accumulation conveyor 22, they are temporarily slowed down or stopped in the accumulation row 32.

[0097] The accumulation conveyor 22 includes, for example, retractable stop fingers 62 for regulating the distribution of the preforms 14 stacked in the accumulation row 32. For example, the stop fingers 62 are mounted to slide transversely between an active position and a retracted position, in which active position the stop fingers extend through the path of the preforms 14 to block their sliding and in which retracted position the preforms 14 are allowed to slide downstream.

[0098] When the stop fingers 62 are in the active position, the preforms 14 stacked at the end of the accumulation conveyor 22 are slowed down or even stopped relative to the speed “V” of the endless flexible element 42 and the friction element 44 slides on the body 24 of the preforms without causing the movement of the endless flexible element 42 to be blocked.

[0099] In both cases, each stopped or moving preform 14 is subjected to a thrust “F”.

[0100] As explained in the preamble, it is very important to correctly adjust the operating parameters of the accumulation conveyor 22 so that the thrust “F” adapts to the dimensions of the preforms 14 being processed.

[0101] As Figure 5 shown, the invention proposes a method for determining the thrust “F” exerted by the friction element 44 of the accumulation conveyor 22 on the preforms 14, the method comprising a first step “E1” of determining the motor torque “Cm” supplied to the endless flexible element 42 and a second step “E2” of estimating the thrust “F” from the motor torque “Cm”.

[0102] In fact, surprisingly, it has been found that the thrust “F” is associated with the motor torque “Cm” by a strictly increasing curve. Thus, an increase or a decrease in the thrust “F” is respectively accompanied by an increase or a decrease in the motor torque “Cm”.

[0103] For example, this correlation can be determined experimentally and then recorded in the memory of the electronic control unit 50 so that the value of the thrust "F" can be correlated with the value of the motor torque "Cm".

[0104] The thrust "F" also depends on the set speed "V" of the accumulation conveyor 22. When it is desired to benefit from a variable-speed accumulation conveyor 22, a graph can be obtained experimentally that gives the relationship between the value of the thrust "F", the motor torque "Cm", and the set speed "V".

[0105] This very advantageously enables the method to be implemented on existing accumulation conveyors 22 without modifying their structure.

[0106] Therefore, there is no longer a need for invasive measurements that require stopping the accumulation conveyor 22 regularly, because the motor torque "Cm" required to advance the endless flexible element 42 at the set speed "V" can be easily measured.

[0107] The thrust can be determined, for example, in a constant manner or it can be determined periodically.

[0108] According to a first embodiment of the invention, the motor torque "Cm" is determined based on the current intensity supplying the electric motor 54 and based on the rotational speed "V" of the endless flexible element 42.

[0109] Since the set speed "V" is usually constant, a simple change in the motor torque "Cm" will reflect a change in the thrust "F" in the same direction.

[0110] Preferably, in order to filter out small variations in the motor torque due to the number of preforms 14 in the accumulation conveyor 22, the thrust "F" is calculated from the motor torque "Cm" measured over a given time period (e.g., from a few seconds to a few minutes).

[0111] For example, the measured values are compared with a reference average value, as well as with an acceptable minimum reference value and a maximum reference value. These reference values are obtained experimentally in a laboratory, for example. For example, the measured values are plotted on a control chart (also known by its English name "control chart"). This control chart is stored, for example, in the electronic control unit, which automatically compares the measured values with the reference values to determine whether the thrust "F" conforms to the optimal operating conditions of the accumulation conveyor 22.

[0112] When the thrust "F" is continuously determined, the motor torque "Cm" can also be determined based on the moving average of the motor torque measured over a given time period.

[0113] Here, the determination of the thrust "F" is done by the electronic control unit 50 based on a signal representing the electrical power consumed by the electric motor 54.

[0114] For example, the motor torque "Cm" is the output data of the software controlling the electronic speed governor 60.

[0115] According to the second embodiment, the motor torque "Cm" is measured by an external torque measuring device 64, which is placed on the torque transmission device between the electric motor 54 and the endless flexible element 42. Such an external torque measuring device 64 is constituted by, for example, a torque meter.

[0116] For example, such an external torque determining device 64 is arranged on the shaft 56 of the drive wheel 46A. The external torque determining device 64 then sends the result of each measurement to the electronic control unit 50 so that it can determine the thrust "F" or the change in the thrust "F".

[0117] Of course, in the case of the first embodiment, it is not necessary to install such an external torque determining device 64 on the accumulation conveyor 22.

[0118] Regardless of which embodiment is adopted, when there is an excessive deviation of the thrust "F" determined in the second step "E2" compared to a reference thrust (such as 5 N), the electronic control unit 50 issues an alarm signal "S".

[0119] By this method, the change in the thrust "F" can be continuously varied during the use of the accumulation conveyor 22 without interrupting production.

[0120] When the alarm signal "S" is issued, various operations may be performed. Either these operations are automatically performed by the electronic control unit 50 when the accumulation conveyor 22 is equipped with appropriate sensors and actuators, or they are performed manually by the operator. For example, sensors for detecting the position of certain components and actuators capable of operating on the position of these components are involved.

[0121] When the alarm signal "S" is issued, for example, the electric motor 54 can be controlled to change the set speed "V" in order to achieve the required thrust "F", thereby avoiding damage to the preform 14 and / or certain components of the manufacturing equipment 10, while not completely stopping production. Depending on the situation, the set speed "V" can be particularly reduced or, conversely, increased.

[0122] When the alarm signal "S" is issued, the spacing between the two tension belts 48 can be checked to verify whether the spacing is well adapted to the dimensions of the preform 14 to be processed. If not, adjustments can be made so as to laterally clamp the preform 14 with an appropriate force, thereby driving the preform 14 with the reference thrust "F". This operation can be performed manually by the operator, or, when the accumulation conveyor 22 is equipped with sensors and actuators suitable for this operation, it can be automatically performed by the electronic control unit 50.

[0123] When the alarm signal “S” is issued, the positions of certain guiding elements of the preform 14, such as the support guide rail 34 or the neck guide 35, can be adjusted manually or automatically to prevent the preform from being stuck by these guiding elements.

[0124] When the alarm signal “S” is issued, it is also possible to verify whether the tension of the tensioning strip 48 is within the optimal operating range.

[0125] With such a method for determining the thrust “F”, it is no longer necessary to frequently disassemble the accumulation conveyor 22 to insert a dynamometer. Therefore, the accumulation conveyor 22 can be equipped with complex and / or fragile elements to perform other operations, such as ultraviolet lamps or LEDs for disinfecting the preforms.

Claims

1. A method for determining the thrust force (F) exerted by an accumulation conveyor (22) on preforms (14), in particular preforms made of thermoplastic material, each preform (14) having a flange (28), the accumulation conveyor (22) comprising: A pair of support rails (34) that support the preform (14) through the flange (28) of the preform, the support rails being for guiding the preform (14) along a path (36); At least one endless flexible element (42), including a friction element (44) that frictions against the preform (14), and a tension strip (48) of the endless flexible element is arranged along the path (36), and the friction element (44) of the drive strip (48) generates a thrust force (F) along the path (36) of the preform by frictional contact against the preform (14); A drive device for the endless flexible element (42), including a motor (54), the motor transmitting a motor torque (Cm) to the endless flexible element (42); Characterized in that the method includes: A first step (E1) of determining the motor torque (Cm) provided to the endless flexible element (42); A second step (E2) of estimating the thrust force (F) based on the motor torque (Cm) determined in the first step (E1).

2. The method according to claim 1, wherein The thrust force (F) is also estimated based on the rotational speed (V) of the endless flexible element (42).

3. The method according to claim 2, wherein The motor is an electric motor (54), and the motor torque (Cm) is determined based on the electric power supplied to the electric motor (54) and the rotational speed (V) of the endless flexible element (42).

4. The method according to claim 3, wherein The power supply to the electric motor (54) is controlled by an electronic speed controller (60), the rotational speed (V) of the endless flexible element (42) is an input set value, and the motor torque (Cm) is the output data of the electronic speed controller (60).

5. The method according to claim 1 or 2, characterized in that, The motor torque (Cm) is determined by measurement using an external torque measuring device (64) placed between the motor (54) and the endless flexible element (42).

6. The method according to any one of the preceding claims, characterized in that, The thrust force (F) is calculated based on the value of the motor torque (Cm) measured over a determination period.

7. The method according to any one of the preceding claims, characterized in that, The correlation between the thrust force (F) and the motor torque (Cm) is determined experimentally.

8. The method according to any one of the preceding claims, characterized in that, When the thrust force (F) determined in the second step (E2) shows an excessive deviation from a reference thrust force, an alarm signal (S) is issued.

9. The method according to claim 8, wherein When the alarm signal (S) is issued, the motor (54) is controlled to change the set speed (V) of the endless flexible element (42) to achieve the desired thrust force (F).

10. The method according to claim 8 or 9, characterized in that, The accumulation conveyor (22) includes two endless flexible elements (42), and the tension strips (48) of the endless flexible elements are arranged on both sides of the path (36) at a determined lateral spacing; and when the alarm signal (S) is issued, the lateral spacing between the two tension strips (48) is checked to verify whether the spacing is well adapted to the dimensions of the preforms (14) to be processed.

11. The method according to any one of claims 8 to 10, characterized in that, When an alarm signal (S) is issued, check the position of the guiding elements of the preform (14), such as the guide rail (34).

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