Apparatus for compression moulding plastic capsules intended for closing containers for liquids.

Abstract

An apparatus (1) for compression moulding plastic objects of concave shape comprises a carousel (2), rotating around a central axis (Z) according to a rotation direction (V), a plurality of forming units (3), each forming unit (3) is positioned on the carousel (2) and includes a male half-mould (31) and a female half-mould (32), at least one of said male half-mould (31) and female half-mould (32) is movable with respect to the other along a moulding axis (S) between an open position and a closed position, to allow the forming unit (3) to move between an open configuration (CA), the half-moulds are spaced, and a closed configuration (CC), the half-moulds are coupled to delimit a forming cavity, an actuator (4), configured to move the at least one movable half-mould between the open position and the closed position, so as to cause the crushing of a dose of plastic interposed therein, the apparatus comprises a transfer device (5), configured to feed the doses to the forming units (3) in a feeding station, a control unit, a safety sensor (11), arranged in a stationary detection site, to interact with the forming units (3) one at a time in succession, the safety sensor is arranged, with respect to the rotation direction (V) of the carousel (2), upstream of the feeding station, at an angular distance () less than 90 degrees therefrom, the safety sensor (11) is connected to the control unit and is configured to detect, for each forming unit (3), an open signal (A), indicative of the fact that the respective movable half-mould of the forming unit (3) is in the open position to the detection site.

Description

[0001] DESCRIPTION

[0002] APPARATUS FOR COMPRESSION MOULDING PLASTIC CAPSULES INTENDED FOR CLOSING CONTAINERS FOR LIQUIDS

[0003] Technical field

[0004] The present invention relates to an apparatus and a method for compression moulding plastic objects of concave shape. For example, the present invention relates to rotary machines for continuously producing plastic capsules, preferably caps or other capsules intended for closing containers for liquids.

[0005] Background art

[0006] Among the solutions known in this field, machines exist which are provided with a main carousel rotating around a vertical axis, on the periphery of which a plurality of moulds are arranged. The moulds are arranged to receive a dose and to form the dose by means of compression, generating the cap. Dose is intended as a portion of semi-solid plastic material, deformable by compression.

[0007] The moulds of the known machines comprise a lower half-mould and an upper half-mould, mutually movable. Usually, one half-mould is fixed and the other half-mould is movable.

[0008] Known solutions are described for example by documents EP4037884A1, US5807592, EP1585623, W00132390A1, W02007017418A2 and W02018051240A1 (on behalf of the same Applicant).

[0009] Moreover, also documents US2012201920, EP3308944, US2009175976 and CN109483843 also describe other solutions in the technical field of compression moulding plastic capsules.

[0010] These documents describe apparatuses for forming caps which have an upper male half-mould, fixed with respect to the carousel, and a lower female half-mould, movable to close against the male mould. The lowerhalf-mould receives the dose in a low position, rises towards the upper half-mould, and, closing the forming cavity, forms the cap. The known apparatuses comprise a further carousel, also rotating around a vertical axis, which has the task of feeding the doses into the mould and extracting the caps from the mould once they have been formed. The described solutions further include a control unit and a hydraulic circuit, connected to each other to manage the multiple electromechanical functions of the apparatus. The hydraulic circuit, inter alia, is in fluid communication with the actuator of the female half-mould, and makes different working pressures available to the actuator as a function of the rotation angle of the carousel.

[0011] In this context, there is a need to increase the productivity of the machines, that is, there is a need to increase the rotation speed of the machine (therefore, increase the moulding speed). The high rotation speed of the machine implies the need for a higher precision, and imposes substantial changes to multiple aspects of the machine itself, such as the sensors, the precision standards, the safety standards and the mechanical, electrical, hydraulic components themselves.

[0012] Furthermore, there is a need to effectively and accurately control the multiple functions of the machine through sensors, which may have diagnostic, safety, or actuation purposes of one or more functions of the machine. For example, solutions such as that described in WO2019207420 (also in the name of the same Applicant) are known, which envisage equipping the apparatus with a camera, in a stationary position with respect to the rotating carousel and designated for displaying the doses deposited in the female half-mould, with the diagnostic purpose of identifying malfunctions of the apparatus. This document also describes a further sensor, a pressure transducer, mounted on board the carousel to detect a pressure value of a line of the hydraulic circuit during the rotation of the carousel.

[0013] Furthermore, solutions are known such as those described by documentsUS2009175976A1 and CN101056748A, which show, inter alia, an apparatus provided with an inductive sensor which has the task of reading a vertical displacement of the movable half-mould along the moulding axis, to correlate it to the mass of the deposited dose to perform quality control. However, the known solutions do not completely solve the problem of effectively and precisely controlling the multiple functions of the machine through sensors. In particular, the known solutions do not solve this problem when the rotation speeds are particularly high. Furthermore, there remains the need to be able to reliably and precisely adjust a series of parameters of the control unit and / or the hydraulic circuit as a function of the position of the movable mould. In fact, the position of the moulds may vary due to the wear of the mechanical components, assembly inaccuracies, or due to different configurations of the apparatus (for example, if the apparatus must pass from the production of one type of cap to another). Furthermore, there is a further need to particularly control the step of lowering the moulds, to prevent, due to malfunctions, the moulds from moving in an unexpected manner and risking colliding with other components, such as the feeding carousel. As mentioned, such problems become more critical when the carousel rotation speeds are high.

[0014] Disclosure of the invention

[0015] An object of the present invention is to provide an apparatus and a method for compression moulding plastic objects of concave shape which overcome the drawbacks of the aforementioned prior art.

[0016] In particular, it is an object of the present invention to provide an apparatus with high productivity, high precision and high safety standards. In particular, it is an object of the present invention to provide an apparatus capable of accurately and precisely detecting and managing one or more operating parameters of the machine. Even more in particular, it is an object of the present invention to provide an apparatuscapable of detecting and managing said one or more parameters as a function of the position of the movable half-mould.

[0017] Said object is fully achieved by the apparatus and by the method for compression moulding which are the object of the present invention, which is characterized by what is contained in the claims below.

[0018] In particular, the present invention provides an apparatus for compression moulding plastic objects of concave shape. As mentioned, preferably the present invention relates to rotating machines for continuously producing plastic capsules, preferably caps. The apparatus comprises a carousel. The carousel is rotatable around a central axis according to a rotation direction. In an example, the rotation direction is a clockwise direction. Preferably, the central axis is a vertical axis. Alternatively, the central axis can be a horizontal axis, i.e., parallel to the ground. The apparatus comprises a plurality of forming units. Each forming unit is positioned on the carousel. Each forming unit is designated for receiving, in input, a dose of material to be formed and sending, in output, the formed capsule. Each forming unit includes a male half-mould and a female half-mould. At least one of said male half-mould and female half-mould is movable with respect to the other along a moulding axis. Preferably, the moulding axis is a vertical axis, parallel to the central axis. In an example, the male halfmould is fixed and the female half-mould is movable along the moulding axis. It should be noted that each forming unit is provided with a moulding axis thereof. Thus, the moulding axes are parallel to each other, and are arranged circumferentially around the central axis. Each forming unit is movable between an open configuration in which the half-moulds are spaced, and a closed configuration, in which the half-moulds are coupled to delimit a forming cavity. The forming cavity is a closed chamber which is created when the half-moulds are closed, and which is occupied by the plastic material which, when compressed, is forced to occupy the entire space of the forming cavity. The apparatus comprises an actuator. The actuator is configured to move the at least one movable half-mouldbetween an open position and a closed position. It should be noted that in the open position the actuator arranges the forming unit in the open configuration, and, in the closed position, the actuator arranges the forming unit in the closed configuration. Thereby, the configuration of the forming unit is such as to cause the crushing of a dose of plastic interposed therein. The apparatus comprises a transfer device. The transfer device is configured to feed the doses to the forming units in a feeding station. In an example, the transfer device is a device rotating with respect to an axis parallel to the central axis. In an example, the transfer device rotates in counter-clockwise direction. Preferably, the transfer device has an upper portion, configured to extract the formed doses, and a lower portion, configured to feed the doses to the forming unit. Preferably, the transfer device has a radial footprint which overlaps a radial footprint of the carousel. That is, in a plan view, the carousel and the transfer device are at least partly overlapping each other. Thereby, the transfer device can "enter" the footprint of the carousel to feed the forming unit with the dose and extract the formed cap. The apparatus comprises a control unit. Preferably, the control unit is designated for setting a set of working parameters related to an operation of the apparatus. For example, the set of parameters can comprise one or more of flow parameters, pressure parameters or other hydraulic parameters, electrical signals, safety signals, rotation speed or further operating parameters of the apparatus. In an example, the apparatus comprises an adjustment sensor. The adjustment sensor is arranged, with respect to the rotation direction of the carousel, downstream of the feeding station, at an angular distance less than 90 degrees therefrom. The adjustment sensor is arranged in a stationary position to interact with the forming units one at a time in succession. That is, by rotating, the carousel makes the forming units available to the adjustment sensor one at a time in succession. In an example, the adjustment sensor is configured to detect, for each forming unit, a closed signal representative of a position along the moulding axis ofthe at least one movable half-mould (for example the female half-mould). For example, the closed signal may correspond to a distance between the female half-mould and the male half-mould. In an example, the movable half-mould performs a closing stroke. In an example, the moving mould performs an opening stroke. The closing stroke is the stroke that the moving mould performs for moving from the open position to the closed position. Therefore, the closing stroke is the stroke performed by the mould for closing the forming chamber thereby forming the dose. The opening stroke is the stroke that the moving mould performs for moving from the closed position to the open position.

[0019] Therefore, the opening stroke is the stroke performed by the mould for opening the forming chamber for releasing the formed dose.

[0020] The closing stroke is performed downstream the feeding station, at an angular distance from the feeding station lower than 90°. The opening stroke is performed upstream the feeding station, at an angular distance from the feeding station lower than 90°.

[0021] Each of the closing stroke and the opening stroke has a (vertical) length in terms of space (and time).

[0022] In an example, the closing stroke comprises a first closing stroke, from the open position to substantially half of the closing stroke, and a second closing stroke, from substantially half of the closing stroke and the closing position. In an example, the closed signal is detected in the second closing stroke of the closing stroke.

[0023] In fact, the adjustment sensor has the aim to detect the phase of closing of the moulds. In particular, the adjustment sensor has the aim to detect the position between the mould in a position that is close to the closing position of the moulds, or at least is in the second closing stroke (the second half of the closing stroke).

[0024] In an example, the opening stroke comprises a first opening stroke, from the closed position to substantially half of the opening stroke, and a second opening stroke, from substantially half of the opening stroke to theopen position. In an example, the opening signal is detected in the second opening stroke of the opening stroke.

[0025] In fact, the safety sensor has the aim to detect the very last phase of the opening of the moulds, to verify that in the stationary detection site the moulds are fully opened and there’s no risk to damage the feeding station. In an example, the control unit is connected to the adjustment sensor. The control unit is programmed to update the set of working parameters depending on the closed signal.

[0026] Due to the high rotation speeds, in fact, there is a need to precisely detect the position of the movable half-mould. Once the position has been detected, this information can be exploited to advantageously update one or more operating parameters of the apparatus. For example, speed, flow or pressure parameters can be changed. The fixed position of the adjustment sensor is particularly advantageous since the sensor can be configured to detect the end part of a stroke of each forming unit and / or of each actuator, from the open configuration to the closed configuration, when the forming unit is near the closed configuration.

[0027] In an example, the angular distance from the adjustment sensor to the feeding station, with respect to the rotation direction of the carousel, is comprised in the range 25° - 50°. Preferably, the angular distance is comprised in the range 29° - 49°. Preferably, the angular distance is equal to 31°. Thereby, the sensor advantageously manages to detect the closed signal in a particular configuration of the forming unit, close to the closed configuration. In fact, following the passage in the feeding station, the forming unit has received the dose, and, therefore, progressively passes from the open configuration to the closed configuration. That is, the adjustment sensor is placed in an angular point of the carousel where the forming unit transits near the closed configuration. Note that positioning the adjustment sensor in an angular position wherein the mould is completely closed could be ineffective. Therefore, the angular distance from the adjustment sensor to the feeding station must consider that themale half-mould and the female half-mould, in the detection point, must be partially open and close to the closed position. In an example, the adjustment sensor is a laser sensor. This type of sensor is particularly advantageous since it is fast and precise and, therefore, also adaptable for carousels rotating at high speed.

[0028] In an example, the apparatus comprises a hydraulic circuit. The hydraulic circuit is configured to feed oil to each actuator of the plurality of forming units. In an example, the hydraulic circuit comprises a delivery line. The delivery line is in communication with a delivery chamber of the actuator. The hydraulic circuit comprises a return line. The return line is in communication with a return chamber of the actuator. The delivery line comprises a high-pressure line and a low-pressure line. The hydraulic circuit includes, for each forming unit, a main valve. The main valve is configured to selectively inhibit or allow the flow of oil from the high-pressure line or from the low-pressure line to the delivery chamber of the respective actuator. The main valve is configured to switch from the low-pressure line to the high-pressure line in an angular zone comprised in the range 25° - 50° from the feeding station, with respect to the rotation direction of the carousel. Thereby, the adjustment sensor is advantageously arranged so as to display the movable half-mould in a point where the actuator of the forming unit switches between two different pressures. Therefore, the angular point wherein the hydraulic circuit switches from low pressure to high pressure is angularly fixed and established by the main valve. Said angular point may be an exchange point. In an example, the control unit is programme to update one or more parameters related to the hydraulic circuit depending on the closed signal. In particular, the control unit may be programmed to update a flow rate parameter of the set of parameters. The flow rate parameter is, for example a parameter representative of a feed rate of the low-pressure line. The control unit is configured to update the flow rate parameter as a function of the closed signal. Thereby, the sensor acts as an input for thecontrol unit, providing it with the closed signal. The control unit is configured to process such a closed signal and update, for example, the low pressure flow rate parameter.

[0029] In this way, for a given exchange (angular) point, a lower flow rate parameter set by the control unit corresponds to a higher distance between the moulds in the exchange point. On the contrary, a higher flow rate parameter set by the control unit corresponds to a lower distance between the moulds in the exchange point.

[0030] By reasoning backwards, it is possible to detect in the given exchange angular point the position of the mould(s) and verify if said position is optimal. If, due to wear and mechanical imprecisions said position is not optimal, it is possible to control (in fact, it is a feedback) the flow rate to assure that the exchange happens in the optimal and wanted position of the moulds.

[0031] Note again that if the adjustment sensor it is not proximal to the exchange point (closed to the closing position) the above-mentioned advantages may not be reached.

[0032] In an example, the apparatus includes a cam. The cam is stationary with respect to the rotation of the carousel and the forming units. The main valve is configured to interact with the cam to selectively inhibit or allow the flow of oil from the high-pressure line or from the low-pressure line to the delivery chamber of the respective actuator. That is, the cam moves the main valve to enable or disable the passage of the high-pressure line and / or the low-pressure line towards the actuator. In an example, the cam is configured to cause the main valve to switch from the low-pressure line to the high-pressure line in the angular zone comprised in the range 25° -50° from the feeding station, with respect to the rotation direction of the carousel. This solution is particularly advantageous since it allows the valve to be managed mechanically. As a function of a cam profile, it is possible to control the valve precisely and move the valve at precise angular intervals of the carousel.In an example, each forming unit comprises a reference element. The reference element is integral with the movable half-mould. The reference element is projecting radially cantilevered, away from the central axis. The reference element has a radial extension. The reference element has an angular extension. In an example, the reference element protrudes radially from the central axis. The safety sensor is configured to detect the angular extension of the reference element.

[0033] The adjustment sensor is configured to detect the reference elements in succession. Thereby, the reference element exits from a plan footprint of the carousel to be displayable by the adjustment sensor.

[0034] In an example, the adjustment sensor is configured to detect a parameter indicative of defects or anomalies of the reference element. For example, the adjustment sensor can detect a surface cleanliness of the reference element (i.e., detect the presence of any dirt). In a further example, the sensor may detect an incorrect positioning with respect to at least one other reference element and / or a displacement in time of the reference element.

[0035] In an example, the adjustment sensor is configured to see the reference elements from the top downwards. The adjustment sensor is further configured to detect a stroke parameter. The stroke parameter is representative of a complete stroke of the reference element, between the open configuration and the closed configuration of the forming unit or vice versa. In such an example, the sensor is particularly advantageous since it can read the reference element both when it is at the open configuration and when it is at the closed configuration. By detecting both configurations, the adjustment sensor communicates with the control unit to calculate the stroke. Such a stroke parameter can be indicative of the stroke of the reference element, the stroke of the actuator, and the stroke of the movable half-mould, the reference element, the actuator, and the movable half-mould being integral with each other. Such a stroke parameter may be used by the control unit to update and / or set one ormore parameters of the set of parameters.

[0036] In an example, the apparatus comprises a support element. The support element is connected to the carousel and to the reference element. The reference element is vertically movable with respect to the support element. The reference element is configured to prevent a rotation of the movable half-mould around the moulding axis.

[0037] In an example, the apparatus comprises a safety sensor. It should be noted that the term "safety" is not intended, in a limiting sense, to a set of features of the safety standards and / or certifications typical of the apparatuses which are the subject of the present invention. Rather, the concept of "safety" is to be understood as a concept of safety internal to the apparatus; that is, the safety sensor has the task of avoiding an undesired operation of the apparatus. The safety sensor is arranged in a stationary detection site. In an example, the safety sensor is positioned externally with respect to a peripheral outline of the carousel. The peripheral outline can be considered as the circumference corresponding to the path followed by the moulds.

[0038] The safety sensor is configured to interact with the forming units one at a time in succession. The external positioning is particularly effective to allow said interaction in space and time succession. Preferably, the detection site is arranged, with respect to the rotation direction of the carousel, upstream of the feeding station, at an angular distance less than 90 degrees therefrom. The safety sensor is connected to the control unit. The safety sensor is configured to detect, for each forming unit, an open signal, indicative of the fact that the respective movable half-mould of the forming unit is in the open position to the detection site.

[0039] Due to the high rotation speeds, there is a need to be certain that the forming unit is in the open configuration before encountering the transfer device. In fact, if for some reason the forming unit was not completely in the open configuration, it would collide with the transfer device.

[0040] The position of the safety sensor is particularly advantageous because thesensor can also detect the end part of a stroke of the sensor from the closed configuration to the open configuration, when the forming unit is near the open configuration. In an example, the angular distance of the detection site from the feeding station is comprised in the range 310° -325°, with respect to the rotation direction of the carousel. Preferably, the angular distance is comprised in the range 315° - 321°. Thereby, the safety sensor advantageously manages to detect the open signal in a particular configuration of the forming unit, close to the open configuration. In fact, before passing into the feeding station, the movable half-mould of the forming unit must prepare to receive the dose, and, therefore, progressively passes from the closed configuration to the open configuration. That is, the safety sensor is placed in an angular point of the carousel where the forming unit transits near the open configuration.

[0041] In an example, the safety sensor is configured to interact without contact with the reference elements of each forming unit in succession. Thereby, each reference element can slide at a predefined distance from the safety sensor, and be detected without contact.

[0042] In an example, the reference element has an extension along a circumferential direction. The circumferential direction is a direction perpendicular to the radial direction of the carousel. The reference element comprises an upper surface and a lower surface. The safety sensor is configured to generate the open signal in response to a presence of the lower surface of the reference element facing the safety sensor. That is, the reference element is configured to slide on the safety sensor, which detects the presence (or absence) thereof. Such a solution is advantageous since, knowing a rotation speed of the carousel, it allows to detect a temporal and / or angular interval corresponding to the passage of the reference element on the sensor.

[0043] In an example, the control unit is configured to measure a duration of the open signal. It should be noted that the duration of the open signal is indicative of how much of the lower surface of the reference element hasbeen detected by the safety sensor. If the reference element passes completely over the sensor for its entire extension, the sensor will detect a first duration. If a subsequent reference element passes on the sensor by a lesser extension than the extension of the lower surface (i.e., passes delayed on the sensor), then the safety sensor will detect a second duration which is less than the first duration.

[0044] In an example, the reference element is provided with a protrusion. The protrusion extends with respect to the reference element along the circumferential direction, in the rotation direction of the carousel. In an example, the reference element comprises an inner portion and an outer portion. The outer portion comprises the protrusion. The outer portion has a first angular extension. The inner portion has a second angular extension. The first angular extension is greater than the second angular extension (in fact, it is a protrusion). Such a protrusion is advantageous since, extending in the rotation direction of the carousel, the sensor detects the reference element in advance with respect to a reference element without the extension.

[0045] In an example, the control unit is provided with a memory. The memory comprises a safety parameter. The safety parameter is representative of a complete passage of the reference element on the safety sensor, for the entire extension of the reference element. For example, the safety parameter corresponds to the first duration. In such an example, the control unit is programmed to compare the safety parameter with each duration of the open signal, corresponding to each passage of each reference element on the safety sensor. On the basis of said comparison, the control unit is configured to update one or more parameters of the set of parameters. In an example, on the basis of said comparison, the control unit is configured to generate an alarm signal. In fact, if the control unit detects that the measured duration is less than the safety parameter, it can generate an alarm. In an example, if the measured duration is less than or equal to 90% of the safety parameter, the control unit can activatesafety measures.

[0046] In an example, on the basis of the open signal (A), the control unit is configured to update a pressure parameter corresponding to the pressure of the return line.

[0047] In fact, it is particularly advantageous, in terms of safety, to know the position of the movable half-mould while it is descending. In particular, there is a desire to be certain that the half-mould has descended before arriving at the feeding station. If not, the half-mould would collide with the dose depositing apparatus, causing serious problems. Therefore, the safety sensor detects a position near the descent of the half-mould, therefore it detects the forming unit in the open configuration or close to the open configuration. In ideal conditions, the machine is designed to lower the movable half-moulds (consequently the reference elements integral therewith), sufficiently in advance. Therefore, in ideal conditions, the safety sensor detects, for each reference element, a duration corresponding to a passage of the reference element for its entire extension, i.e., a complete passage. If the reference element delays the descent, it progressively reaches the safety sensor so that the safety sensor detects a smaller extension. The smaller the extension detected, the later the reference element descends. In an extreme case in which the reference element greatly delays the descent, and descends after the sensor, the sensor may not detect the passage of the reference element. To avoid this, when the sensor detects an extension less than the complete extension (for example it detects an extension less than 90% of the complete extension), the control unit generates the alarm signal and / or acts with a safety measure. For example, a safety measure may correspond to a stop of the rotation of the carousel, commanded by the control unit. Alternatively, or in combination, a safety measure may correspond to a displacement of the transfer device from an operating position to a non-interference position.

[0048] In an example, the safety sensor is an inductive sensor. This type ofsensor is particularly economical and allows the aforementioned functions to be carried out in a practical and effective manner.

[0049] According to an aspect of the present description, the present invention provides a method for compression moulding plastic objects of concave shape. The method comprises a step of arranging a carousel, rotating around a central axis according to a rotation direction. The method comprises a step of arranging a plurality of forming units, positioned on the carousel. Each forming unit includes a male half-mould and a female halfmould. At least one of said male half-mould and female half-mould is movable with respect to the other along a moulding axis between an open position and a closed position, to allow the forming unit to move between an open configuration, in which the half-moulds are spaced, and a closed configuration, in which the half-moulds are coupled to delimit a forming cavity. Each forming unit includes an actuator. The actuator is configured to move the at least one movable half-mould between the open position and the closed position, so as to cause the crushing of a dose of plastic interposed therein. The method comprises a step of arranging a control unit, designated for setting a set of working parameters related to an operation of the apparatus.

[0050] In an example, the method comprises a step of arranging an adjustment sensor. The adjustment sensor is arranged, with respect to the rotation direction of the carousel, downstream of the feeding station, at an angular distance less than 90 degrees therefrom, in a stationary position to interact with the forming units one at a time in succession. The method comprises a step of detecting, by means of the adjustment sensor, a closed signal. The closed signal is representative, for each forming unit, of a position along the moulding axis of the at least one movable half-mould. The method comprises a step of updating, by means of the control unit, the set of working parameters depending on the closed signal.

[0051] In an example, the method comprises a step of detecting, by means of the adjustment sensor, the forming unit in the closed configuration. In anexample, the method comprises a step of detecting, by means of the adjustment sensor, the forming unit in the open configuration. In an example, the method comprises a step of calculating a stroke parameter. The stroke parameter is representative of the distance between the halfmoulds when they are in the open configuration.

[0052] In an example, on the basis of the stroke parameter, the control unit updates a pressure parameter and / or a flow rate parameter of the set of parameters.

[0053] In a further example, the control unit, in response to a start command of the apparatus, performs a start cycle. The start cycle includes a step of executing at least one complete rotation of the carousel with the actuators in the open position. The start cycle includes a step of executing at least one complete rotation of the carousel with the actuators in the closed position.

[0054] It should be noted that, in such an example, the start cycle comprises a calibration procedure of one or more sensors, including, for example, the adjustment sensor. "Start cycle" is not to be understood, exclusively, as a start cycle for the production of caps. The calibration procedure of one or more sensors can occur regardless of the start of machine production (i.e., it can be a cycle in itself). Alternatively, the sensor calibration procedure may coincide with the production start procedure (i.e., by default, when production begins, the calibration procedure is performed). In a further alternative example, the sensor calibration procedure can occur on request in one or more instants during the cap production steps.

[0055] In an example, the method comprises a step of arranging a safety sensor. The safety sensor is arranged in a stationary detection site to interact with the forming units one at a time in succession. The detection site is arranged, with respect to the rotation direction of the carousel, upstream of the feeding station, at an angular distance less than 90 degrees therefrom. The method comprises a step of detecting, by means of the safety sensor, an open signal. The open signal is indicative of the fact that, for eachforming unit, the respective movable half-mould of the forming unit is in the open position to the detection site.

[0056] In an example, each forming unit comprises a reference element, integrally connected to the movable half-mould. In such an example, the safety sensor detects an extension of the reference element along a circumferential direction. In an example, the safety sensor generates the open signal in response to a presence of a lower surface of the reference element facing the safety sensor.

[0057] In an example, the safety sensor is connected to the control unit. The method comprises a step of detecting a duration of the open signal. The open signal represents the rotation angle for which the reference element interacts with the safety sensor without contact.

[0058] In an example, the control unit commands a stop of the rotation of the carousel. Alternatively, or in combination, the control unit commands a displacement of the transfer device from an operating position to a noninterference position, in response to the open signal. For example, the transfer device can quickly exit from the footprint operating position, towards a non-interference position in which, if the moulds are not completely lowered, they would not collide with the transfer device.

[0059] Brief description of drawings

[0060] These and other features will become more apparent from the following description of a preferred embodiment, illustrated purely by way of nonlimiting example in the accompanying drawings, wherein:

[0061] - Figure 1 illustrates an apparatus for compression moulding plastic objects of concave shape;

[0062] - Figure 2 illustrates a view from above of the apparatus;

[0063] - Figure 3 illustrates a safety sensor;

[0064] - Figure 4 illustrates an adjustment sensor;

[0065] - Figure 5 illustrates a trend of a position of a movable half-mould of the apparatus, in relation to a rotation angle of a carousel of the apparatus;- Figure 6 schematically illustrates a passage of a reference element above the safety sensor and a time trend diagram of the signal detected by the safety sensor.

[0066] Detailed description of preferred embodiments of the invention According to an aspect of the present description, an apparatus for compression moulding plastic objects of concave shape, preferably caps, is indicated with 1. The apparatus 1 comprises a carousel 2, rotating around a central axis Z according to a rotation direction V. The carousel is rotatably connected to a base 100. The base 100 comprises a first portion 101, connected to the wheel. The base 100 comprises a second portion 102 and a third portion 103. The second portion 102 and the third portion 103 extend in a direction parallel to the main axis Z. Preferably, the second portion 102 and the third portion 103 extend vertically. Preferably, the central axis Z is a vertical axis. In an example, the rotation direction V is a counter-clockwise direction. The apparatus 1 comprises a plurality of forming units 3. Each forming unit 3 is positioned on the carousel 2. Each forming unit 3 is designated for receiving, in input, a dose of material to be formed and sending, in output, the formed capsule. Each forming unit 3 includes a male half-mould 31 and a female half-mould 32. At least one of said male half-mould 31 and female half-mould 32 is movable with respect to the other along a moulding axis S. Preferably, the moulding axis S is a vertical axis. The moulding axis S is parallel to the central axis Z. In an example, the male half-mould 31 is fixed and the female half-mould 32 is movable along the moulding axis S. Each forming unit 3 is provided with a moulding axis S thereof, and is arranged circumferentially, around the central axis Z. Each forming unit 3 is movable between an open configuration CA in which the half-moulds are spaced, and a closed configuration CC, in which the half-moulds are coupled to delimit a forming cavity. The apparatus comprises an actuator 4. The actuator 4 is configured to move the at least one movable half-mould between an openposition and a closed position. The open position of the actuator 4 corresponds to the open configuration CA of the forming unit 3. The closed position of the actuator 4 corresponds to the closed configuration CC of the forming unit 3. The apparatus comprises a transfer device 5. The transfer device 5 is configured to feed the doses to the forming units 3 in a feeding station. In an example, the transfer device 5 is a device rotating with respect to an axis parallel to the central axis Z. Preferably, the transfer device 5 has an upper portion, configured to extract the formed doses, and a lower portion, configured to feed the doses to the forming unit 3. Preferably, the transfer device 5 has a radial footprint which overlaps a radial footprint of the carousel. That is, in a plan view (see, by way of non-limiting example, Figure 2), the carousel 2 and the transfer device 5 are overlapping each other. The apparatus 1 comprises a control unit. Preferably, the control unit is designated for setting a set of working parameters related to an operation of the apparatus 1. For example, the set of parameters can comprise one or more of flow parameters, pressure parameters or other hydraulic parameters, electrical signals, safety signals, rotation speed or further operating parameters of the apparatus. In an example, the apparatus 1 comprises an adjustment sensor 10. The adjustment sensor 10 is arranged, with respect to the rotation direction V of the carousel 2, downstream of the feeding station, at an angular distance oc less than 90 degrees therefrom. The adjustment sensor 10 is arranged in a stationary position to interact with the forming units 3 one at a time in succession. In an example, the adjustment sensor 10 is connected to a support bracket. In an example, the adjustment sensor 10 is connected to the second portion 102 of the base 100. In an example, the support bracket is configured to connect the adjustment sensor 10 to the second portion 102 of the base 100. In such an example, the support bracket projects from the second portion 102 so that the adjustment sensor 10 is mounted cantilevered with respect to the second portion 102. In an example, the adjustment sensor 10 is configured to detect, for eachforming unit 3, a closed signal representative of a position along the moulding axis S of the at least one movable half-mould (for example the female half-mould 32). In an example, the control unit is connected to the adjustment sensor 10. The control unit is programmed to update the set of parameters depending on the closed signal.

[0067] In an example, the angular distance oc from the adjustment sensor 10 to the feeding station, with respect to the rotation direction V of the carousel 2, is comprised in the range 25° - 50°. Preferably, the angular distance oc is equal to 31°.

[0068] In an example, the adjustment sensor 10 is a laser sensor.

[0069] In an example, the apparatus comprises a hydraulic circuit, configured to feed oil to each actuator 4 of the plurality of forming units 3. In an example, the hydraulic circuit comprises a delivery line, in communication with a delivery chamber of the actuator 4, and a return line, in communication with a return chamber of the actuator 4. The delivery line comprises a high-pressure line and a low-pressure line. The hydraulic circuit includes, for each forming unit 3, a main valve, configured to selectively inhibit or allow the flow of oil from the high-pressure line or from the low-pressure line to the delivery chamber of the respective actuator 4. The main valve is configured to switch from the low-pressure line to the high-pressure line in an angular zone comprised in the range 25° - 50° from the feeding station, with respect to the rotation direction V of the carousel 2.

[0070] In an example, the control unit is programmed to update a flow rate parameter of the set of parameters. The flow rate parameter is a parameter representative of a feed rate of the low-pressure line. The control unit is configured to update the flow rate parameter as a function of the closed signal. In an example, the control unit is configured to process such a closed signal and update, for example, the low pressure flow rate parameter.

[0071] In the following, with reference to Figure 5, byway of non-limiting example,a trend of a displacement of the actuator between the open position and the closed position will be described.

[0072] The graph depicted indicates a displacement of the actuator 4 between the open position and the closed position, as a function of a rotation angle of the carousel 2. The trend of the actuator 4 comprises a section ascending from the open position towards the closed position. The ascending section comprises a first section A1 , in which the actuator 4 is fed with oil coming from the low-pressure line, and a second section A2, in which the actuator 4 is fed with oil coming from the high-pressure line. It should be noted that the adjustment sensor 10 is positioned at the variation between the first section A1 and the second section A2. The trend comprises a third section A3 in which the actuator is in the closed position. Substantially, such a section corresponds to the step in which the dose is crushed in the forming cavity. The trend of the actuator 4 comprises a section descending from the closed position towards the open position. The descending section comprises a fourth section A4, in which the actuator 4 gradually descends so as not to tear the newly formed dose, and a fifth section A5, in which a chamber of the actuator 4 is unloaded to quickly lower the actuator and bring it into the open position. The trend comprises a sixth section A6, corresponding to the step in which the actuator 4 is in the open position and receives the dose from the transfer device 5.

[0073] The control unit can adjust a flow rate parameter as a function of the closed signal. For example, the control unit can decrease the feeding flow rate of the low-pressure line of the actuator 4. In such a case, the trend of the actuator is characterized by a further first section A1 ’, indicative of a lower ascending speed towards the closed position with respect to that of the first section A1. Accordingly, the trend of the actuator is characterized by a further second section A2’, parallel to the second section A2. Thereby, the control unit can control an exchange height. That is, the control unit can control the position along the moulding axis S in which theswitching between low pressure and high pressure can occur. In fact, the angular switching position is controlled and defined mechanically and is, therefore, preset.

[0074] In an example, the apparatus 1 includes a cam. The cam is configured to control said angular switching position. The cam is stationary with respect to the rotation of the carousel 2 and the forming units 3. The main valve is configured to interact with the cam to selectively inhibit or allow the flow of oil from the high-pressure line or from the low-pressure line to the delivery chamber of the respective actuator 4. That is, the cam moves the main valve to enable or disable the passage of the high-pressure line and / or the low-pressure line towards the actuator 4. In an example, the cam is configured to cause the main valve to switch from the low-pressure line to the high-pressure line in the angular zone comprised in the range 25° - 50° from the feeding station, with respect to the rotation direction V of the carousel 2.

[0075] In an example, each forming unit 3 comprises a reference element 7, integral with the movable half-mould. The reference element 7 is projecting radially cantilevered, away from the central axis Z. The adjustment sensor 10 is configured to detect the reference elements 7 in succession. In an example, the laser adjustment sensor 10 is configured to detect a parameter indicative of the surface cleanliness of the reference element 7. In an example, the adjustment sensor 10 is configured to see the reference elements 7 from the top downwards. The adjustment sensor 10 is further configured to detect a stroke parameter. The stroke parameter is representative of a complete stroke of the reference element 7, between the open configuration and the closed configuration of the forming unit 3 or vice versa. Such a stroke parameter may be used by the control unit to update and / or set one or more parameters of the set of parameters.

[0076] Therefore, in an example, the control unit performs a step of calculating the stroke parameter. In such an example, the control unit updates a pressure parameter and / or a flow rate parameter of the set of parameters.In an example, the apparatus comprises a support element 9. The support element 9 is connected to the carousel 2 and to the reference element 7. The reference element 7 is vertically movable with respect to the support element 9. The reference element 7 is configured to prevent a rotation of the movable half-mould around the moulding axis S. In an example, the support element 9 is a cylindrical element, having a vertical extension along a direction parallel to the moulding direction. The support element 9 is mounted on the carousel 2. In an example, the reference element 7 is configured to couple to the support element 9 through a hole. Thereby, the reference element 7 can slide vertically along the reference element 7, preventing a rotation of the movable half-mould around the moulding axis S.

[0077] In an example, the apparatus 1 comprises a safety sensor 11 , arranged in a stationary detection site. The safety sensor 11 is configured to interact with the forming units 3 one at a time in succession. In an example, the safety sensor 11 is connected to the first portion 101 of the base 100. Preferably, the detection site is arranged, with respect to the rotation direction V of the carousel 2, upstream of the feeding station, at an angular distance £ less than 90 degrees therefrom. The safety sensor 11 is connected to the control unit and is configured to detect, for each forming unit 3, an open signal A, indicative of the fact that the respective movable half-mould of the forming unit 3 is in the open position to the detection site.

[0078] In an example, the angular distance £ of the detection site from the feeding station is comprised in the range 310° - 325°, with respect to the rotation direction of the carousel. That is, the angular distance £ of the detection site from the feeding station is comprised in the range -35° - -50°, upstream of the feeding station.

[0079] In an example, the safety sensor 11 is configured to interact without contact with the reference elements 7 of each forming unit 3 in succession. In an example, the reference element 7 has an extension E along acircumferential direction. The circumferential direction is a direction perpendicular to the radial direction of the carousel 2. The reference element 7 comprises an upper surface 72 and a lower surface 73. The safety sensor 11 is configured to generate the open signal A in response to a presence of the lower surface 73 of the reference element 7 facing the safety sensor 11.

[0080] In an example, the control unit is configured to measure a duration D1 of the open signal A. It should be noted that the duration D1 of the open signal A is indicative of how much lower surface 73 of the reference element 7 has been detected by the safety sensor 11 (i.e., how much lower surface 73 has transited on the sensor 11).

[0081] In an example, the reference element 7 is provided with a protrusion 71. The protrusion 71 extends with respect to the reference element 7 along the circumferential direction, in the rotation direction V of the carousel 2. If the reference element 7 passes completely over the safety sensor 11 for its entire extension E, the sensor will detect a first duration D1. If a subsequent reference element passes on the sensor 11 by a lesser extension than the complete extension of the lower surface (i.e., passes delayed on the sensor), then the safety sensor 11 will detect a second duration D2 which is less than the first duration D1. In an example, the control unit is provided with a memory. The memory comprises a safety parameter, representative of a complete passage of the reference element 7 on the safety sensor 11, for the entire extension E of the reference element. For example, the safety parameter corresponds to the first duration D1. In such an example, the control unit is programmed to compare the safety parameter with each duration of the open signal A, corresponding to each passage of each reference element 7 on the safety sensor 11. On the basis of said comparison, the control unit is configured to update one or more parameters of the set of parameters. In an example, on the basis of said comparison, the control unit is configured to generate an alarm signal. In an example, if the measured duration is lessthan or equal to 90% of the safety parameter, the control unit can activate safety measures.

[0082] In an example, on the basis of the open signal A, the control unit is configured to update a pressure parameter corresponding to the pressure of the return line.

[0083] For example, a safety measure may correspond to a stop of the rotation of the carousel 2, commanded by the control unit. Alternatively, or in combination, a safety measure may correspond to a displacement of the transfer device 5 from an operating position to a non-interference position. In an example, the safety sensor 11 is an inductive sensor. In said example, the detection is performed when also the second stroke is completed.

[0084] In a further example, the control unit, in response to a start command of the apparatus, performs a start cycle. The start cycle includes a step of executing at least one complete rotation of the carousel 2 with the actuators 4 in the open position. The start cycle includes a step of executing at least one complete rotation of the carousel 2 with the actuators in the closed position. In an example, the stroke calculation occurs on the basis of the detection of the actuators 4 in the closed position and in the open position. That is, the control unit calculates the stroke by subtracting the detected distance of the actuator 4 in the closed position from the detected distance of the actuator 4 in the open position. In a further example, the control unit performs the following steps:

[0085] - commands the carousel 2 to perform a plurality of complete rotations with the actuators 4 in the open position;

[0086] - commands the carousel 2 to perform a plurality of complete rotations with the actuators 4 in the closed position;

[0087] - calculates a plurality of strokes indicative of one or more passages of the actuator 4 in the closed and open position.

[0088] - averages the strokes to find an average stroke parameter.

[0089] In an example, the control unit detects the duration D1 of the open signalA. In an example, the control unit commands a stop of the rotation of the carousel 2 and / or a displacement of the transfer device 5 from an operating position to a non-interference position, in response to the open signal.

Claims

CLAIMS1. An apparatus (1) for compression moulding plastic objects of concave shape, comprising:- a carousel (2), rotating around a central axis (Z) according to a rotation direction (V);- a plurality of forming units (3), each forming unit (3) being positioned on the carousel (2) and includinga male half-mould (31) and a female half-mould (32), wherein at least one of said male half-mould (31) and female half-mould (32) is movable with respect to the other along a moulding axis (S) between an open position and a closed position, to allow the forming unit (3) to move between an open configuration (CA), in which the half-moulds are spaced, and a closed configuration (CC), in which the half-moulds are coupled to delimit a forming cavity;an actuator (4), configured to move the at least one movable halfmould between the open position and the closed position, so as to cause the crushing of a dose of plastic interposed therein;- a transfer device (5), configured to feed the doses to the forming units (3) in a feeding station;- a control unit;- a safety sensor (11), arranged in a stationary detection site, for interacting with the forming units (3) one at a time in succession, characterized in that the detection site is arranged, with respect to the rotation direction (V) of the carousel (2), upstream of the feeding station, at an angular distance (£) less than 90 degrees therefrom, and in that the safety sensor (11) is connected to the control unit and is configured to detect, for each forming unit (3), an open signal (A), indicative of the fact that the respective movable half-mould of the forming unit (3) is in the open position to the detection site.

2. The apparatus (1) according to claim 1 , wherein the angular distance (£)of the detection site from the feeding station is comprised in the range 310° - 325°, with respect to the rotation direction (V) of the carousel (2).

3. The apparatus (1) according to claim 2, wherein each forming unit (3) comprises a reference element (7), integrally connected to the movable half-mould, and wherein the safety sensor (11) is configured to interact without contact with the reference elements of each forming unit (3) in succession.

4. The apparatus (1) according to claim 3, wherein the reference element (7) has an extension (E) along a circumferential direction and comprises an upper surface (72) and a lower surface (73), the safety sensor (11) being configured to generate the open signal (A) in response to a presence of the lower surface (73) of the reference element facing the safety sensor (11).

5. The apparatus (1) according to claim 4, wherein the control unit is configured to measure a duration (D1) of the open signal (A) and wherein the reference element is provided with a protrusion (71), which extends with respect to the reference element (7) along the circumferential direction, in the rotation direction (V) of the carousel.

6. The apparatus (1) according to claim 5, wherein the control unit is provided with a memory, and wherein the memory comprises a safety parameter, representative of a complete passage of the reference element on the safety sensor, for the entire extension (E) of the reference element, and wherein the control unit is programmed to compare the safety parameter with the duration (D1) of the open signal (A) , and, on the basis of said comparison, update one or more parameters of the set of parameters.

7. The apparatus (1) according to claim 6, wherein, on the basis of said comparison, the control unit is configured to generate an alarm signal.

8. The apparatus (1) according to any one of the preceding claims, comprising a hydraulic circuit, configured to feed oil to the actuators (4) of the plurality of forming units (3), and wherein the hydraulic circuitcomprises a delivery line, in communication with a delivery chamber of the actuator (4), and a return line, in communication with a return chamber of the actuator (4), wherein, on the basis of the open signal (A), the control unit is configured to update a pressure parameter corresponding to the pressure of the return line.

9. The apparatus (1) according to any one of the preceding claims, comprising an adjustment sensor (10), arranged, with respect to the rotation direction (V) of the carousel (2), downstream of the feeding station, at an angular distance (a) less than 90 degrees therefrom, in a stationary position to interact with the forming units (3) one at a time in succession, and configured to detect, for each forming unit (3), a closed parameter representative of a position of the at least one movable halfmould along the moulding axis (S).

10. The apparatus (1) according to any one of claims 3 to 9, comprising a support element (9), connected to the carousel (2) and to the reference element (7), so that the reference element (7) is vertically movable with respect to the support element (9), the reference element (7) being further configured to prevent a rotation of the movable half-mould around the moulding axis (S).

11. The apparatus (1) according to any one of the preceding claims, wherein the safety sensor (11) is an inductive sensor.

12. The apparatus (1) according to any one of the preceding claims, wherein the safety sensor (11) is positioned externally with respect to a peripheral outline of the carousel.

13. A method for compression moulding plastic objects of concave shape, comprising the following steps:- arranging a carousel (2), rotating around a central axis (Z) according to a rotation direction (V) and a plurality of forming units (3), each forming unit (3) being positioned on the carousel (2) and includinga male half-mould (31) and a female half-mould (32), wherein at least one of said male half-mould (31) and female half-mould (32) ismovable with respect to the other along a moulding axis (S) between an open position (CA) and a closed position (CC), to allow the forming unit (3) to move between an open configuration (CA), in which the half-moulds are spaced, and a closed configuration (CC), in which the half-moulds are coupled to delimit a forming cavity;an actuator (4), configured to move the at least one movable halfmould between the open position and the closed position, so as to cause the crushing of a dose of plastic interposed therein;- arranging a transfer device (5), configured to feed the doses to the forming units (3) in a feeding station;- arranging a control unit;- arranging a safety sensor (11), arranged in a stationary detection site, to interact with the forming units (3) one at a time in succession, the detection site being arranged, with respect to the rotation direction (V) of the carousel (2), upstream of the feeding station, at an angular distance (P) less than 90 degrees therefrom;- detecting, by means of the safety sensor (11), an open signal (A), indicative of the fact that, for each forming unit (3), the respective movable half-mould of the forming unit (3) is in the open position to the detection site.

14. The method according to claim 13, wherein each forming unit (3) comprises a reference element (7), integrally connected to the movable half-mould, and wherein the safety sensor (11) detects an extension (E) of the reference element (7) along a circumferential direction, and wherein the safety sensor (11) generates the open signal (A) in response to a presence of a lower surface (73) of the reference element (7) facing the safety sensor (11).

15. The method according to claim 14, wherein the safety sensor (11) is connected to the control unit and detects a duration (D1) of the open signal (A), the open signal (A) being representative of the rotation angle for which the reference element (7) interacts without contact with thesafety sensor (11).

16. The method according to any one of claims 13 to 15, wherein the control unit commands a stop of the rotation of the carousel (2) and / or a displacement of the transfer device (5) from an operating position to a non-interference position, in response to the open signal (A).

17. The method according to any of the claims from 13 to 16, wherein the movable half-mould performs an opening stroke from the closed position to the open position, the opening stroke comprising a first opening stroke, from the closed position to substantially half of the opening stroke, and a second opening stroke, from substantially half of the opening stroke to the open position, and wherein the opening signal is detected in the second opening stroke of the opening stroke.

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