Patent Description:
In particular, the invention refers to a control method for controlling a thermoforming machine intended to process an article made of plastics, in particular an article made of thermoplastic material.

Thermoforming machines are known that are intended to thermoform a blank product made of thermoplastic material, for example in the form of a slab, sheet or film, to make a finished thermoformed product such as a suitcase shell, a part of a household appliance, an item of sporting equipment, a part of a vehicle, a bathtub and the like. Such thermoforming machines comprise one or more heating devices and forming means. The heating devices each comprise a plurality of heating elements, such as resistances, to heat and soften the blank product so as to set up the blank product to be formed as a finished product by suitable forming means.

The softened product, i.e. the intermediate product, can take on, according to circumstances, a substantially regular shape, for example similar to a half-bubble or half-ball, also called a "bubble" or a substantially irregular shape.

The shape of the intermediate product and the shape of the thermoformed product are a function of dimensions and of the material of the blank product and of shaping and temperature conditions applied to the product in processing.

One known thermoforming method comprises a setting step of setting a series of control parameters for controlling the thermoforming machine, i.e. a thermoforming "recipe", for controlling the heating devices and/or the forming means. The machine parameters comprise for example thermal power values supplied by the heating devices and/or the respective supplying time of this thermal power. The setting step is performed by a specialized operator who on the basis of his or her experience programs the thermoforming machine.

Nevertheless, owing to the multiple variables involved in the processing, the definitive control parameters are achieved after a series of production tests which result in rejects. <CIT>, <CIT>, and <CIT> disclose thermoforming methods for controlling a thermoforming machine.

One drawback of the known thermoforming method is the fact of long setting times for the thermoforming machine.

One defect of the known thermoforming method is that in order to run a thermoforming machine efficiently, specialized personnel must be available.

One defect of the thermoforming method disclosed above is that it is unable to ensure over time satisfactory quality stability of production.

One object of the present invention is to improve thermoforming methods for controlling a thermoforming machine.

One object is to provide a thermoforming method for controlling a thermoforming machine that is effective regardless of the experience of the operator.

One object is to provide a thermoforming method for controlling a thermoforming machine that enables the qualitative stability of production to be improved with respect to known methods.

One object is to improve a thermoforming system comprising a thermoforming machine.

One object is to optimize processing of an article to be thermoformed on the basis of a through estimate of the control parameters and of continuous monitoring of the article being processed.

One advantage is to obtain simply a thermoformed article of quality by selecting a reduced number of start parameters.

A further advantage is considering environmental variables to calculate accurately the control parameters of the thermoforming machine.

Such objects and advantages and still others are achieved by a thermoforming method for controlling a thermoforming machine and by a thermoforming system comprising the thermoforming machine, as disclosed in one or more of the claims set out below.

In one embodiment according to the invention, a thermoforming method for controlling a thermoforming machine for processing an article made of thermoplastic material comprises: setting at least one start parameter, the start parameter comprising a parameter that is related to the processing of the article; estimating at least one operating parameter of the thermoforming method on the basis of the at least one start parameter; calculating at least one control parameter to control the thermoforming machine on the basis of the operating parameter; detecting at least one actual parameter of the thermoforming method; comparing the at least one actual parameter detected with the at least one operating parameter; on the basis of the comparing, modifying the at least one control parameter; wherein detecting, comparing and modifying are in a cyclical sequence.

The invention can be better understood and actuated with reference to the attached drawings that illustrate an embodiment thereof by way of non-limiting example, in which:.

With reference to the attached figures, with numeric reference <NUM> a thermoforming machine is indicated that is arranged for thermoforming an article <NUM>, <NUM>, <NUM> made of thermoplastic material. The article <NUM>, <NUM>, <NUM>, comprises a blank product <NUM>, for example in the form of a slab, sheet or film, or an intermediate product <NUM>, a so-called "bubble", or a thermoformed product <NUM>, i.e. a finished product, also known as a drawn product, like for example a suitcase shell, an item of sporting equipment, a tank, a vehicle part, a part of a household appliance and the like. In the specific embodiment shown in the figures, the intermediate product <NUM> is obtained in a pressure shaping step of pressure shaping of the heated blank product <NUM> (<FIG>), whereas the thermoformed product <NUM> is obtained in a shaping under vacuum step of shaping under vacuum the intermediate product <NUM> (<FIG>).

A slab or sheet is a body that has two prevalent dimensions with respect to the third and which is bounded by two opposite surfaces situated at a reciprocal distance, for example the thickness of the slab or sheet, which is relatively small.

The article <NUM>, <NUM>, <NUM> may be virtually divided into a plurality of areas. Each area, during processing, i.e. during the application of the thermoforming method, is associated with an operating parameter of the thermoforming method, i.e. with a start parameter P1 and/or with an operating parameter P2 and/or with a control parameter P3 and/or with an actual parameter PR which will be disclosed below. As, as mentioned, the article <NUM>, <NUM>, <NUM> is transformed in the steps of the thermoforming method, this area may not maintain the same shape during processing. Nevertheless, the skilled person will have no difficulty understanding which area of the article <NUM>, <NUM>, <NUM> is being referred to each time.

The thermoforming machine <NUM> may be a numerical control machine.

The thermoforming machine <NUM> is included in a thermoforming system disclosed below.

The thermoforming machine <NUM> may comprise, in particular, on a support frame, a support plane <NUM> for supporting the blank product <NUM>, for example for supporting the blank product <NUM> in a horizontal position (<FIG> and <FIG>).

The thermoforming machine <NUM> comprises controllable forming means for forming the article <NUM>, <NUM>, <NUM>. Such forming means comprises a forming mould, for example positioned below the support plane <NUM>. On the forming mould, a contact surface is obtained that is intended to come into contact with the intermediate product <NUM> to be formed. The contact surface is arranged for imprinting the shape thereof on the intermediate product <NUM>. The forming mould may be movable with respect to the support plane <NUM> approaching and/or moving away from the article <NUM>, <NUM>, <NUM>.

The thermoforming machine <NUM> comprises at least one heating device <NUM>, <NUM> facing a surface of the article <NUM>, <NUM>, <NUM> and arranged, in use, for heating this surface of the article <NUM>, <NUM>, <NUM>. In particular, with reference to <FIG>, the thermoforming machine <NUM> comprises an upper heating device <NUM> and a lower heating device <NUM>, where upper and lower refer to the position of the article <NUM>, <NUM>, <NUM> on the support plane <NUM>. The upper heating device <NUM> and the lower heating device <NUM> are shown schematically in <FIG>, and are movable towards/away from one another to heat, in particular soften, the article <NUM>, <NUM>, <NUM>.

The upper <NUM> and lower <NUM> heating devices each comprise a plurality of respective heating elements <NUM>, shown schematically in the form of rectangles in <FIG>, for example comprising resistances, in particular quartz or ceramic or halogen resistances.

In particular, in use, each heating element <NUM> is controllable for heating, in a heating step, the corresponding area of the article <NUM>, <NUM>, <NUM> facing each heating element <NUM>.

The forming means comprises fluid supplying means, which is not illustrated, which is controllable to supply a fluid on the article <NUM>, <NUM>, <NUM>, in particular on the heated blank product <NUM>. The fluid supplying means is connectable, in use to a compressed fluid supplying device and comprises one or more shaped nozzles to be traversed by a fluid, for example air. The fluid supplying means is positioned below the article <NUM>, <NUM>, <NUM> to be thermoformed.

The forming means further comprises suction means, which is not illustrated, which is controllable to generate a vacuum between the intermediate product <NUM> and the contact surface of the forming mould to make the article <NUM>, <NUM>, <NUM> adhere to the contact surface. The suction means is connected to a device for generating a vacuum, such as a vacuum pump. The suction means comprises one or more further shaped nozzles to be traversed by a fluid, for example air. The suction means is positioned below the article <NUM>, <NUM>, <NUM> to be thermoformed.

In an alternative embodiment, the thermoforming machine comprises supplying/suction means provided with the same nozzles alternately connected to the compressed fluid supplying device and to the device for generating the vacuum, to dispense the compressed fluid and to generate the vacuum on the article <NUM>, <NUM>, <NUM>.

The thermoforming machine <NUM> comprises detecting means <NUM>, <NUM> configured for detecting the at least one actual parameter PR (<FIG>). The at least one actual parameter PR comprises, in particular, an actual temperature value TR detected on the area of the article <NUM>, <NUM>, <NUM>. The detecting means <NUM>, <NUM> comprises, in particular, temperature <NUM> detecting means for measuring the actual temperature value TR. The temperature <NUM> detecting means may comprise a thermographic camera or other contactless temperature detecting means of the infrared radiation type. The actual temperature value TR may be included in a matrix of detected actual temperature values, wherein each element of the matrix is associated with a respective area of the article <NUM>, <NUM>, <NUM>.

In addition or alternatively to the actual temperature value TR, the at least one actual parameter PR may comprise an actual position X of a point of the article <NUM>, <NUM>, <NUM>.

The detecting means <NUM>, <NUM> comprises, in particular, position detecting means <NUM> for measuring an actual position X. The position detecting means <NUM> may comprise a depth camera or video camera or other contactless means for detecting position by laser or stereoscopy. The actual position X may be included in a matrix of actual detected positions, in which each element of this matrix is associated with a respective point of the article <NUM>, <NUM>, <NUM>.

The thermoforming system comprises sensor means <NUM> configured for detecting at least one environmental parameter in a work environment W in which the thermoforming machine <NUM> is located (<FIG>). The work environment may comprise a room or an industrial shed.

The at least one environmental parameter comprises, in particular, an ambient temperature value of the work environment W. The sensor means <NUM> comprises, in particular, a temperature probe, like a thermocouple, to detect the ambient temperature value.

In addition or alternatively to the ambient temperature value, the at least one environmental parameter may comprise an ambient humidity value, in particular a relative humidity value, of the work environment W, in particular of the air of the work environment W. The sensor means <NUM> comprises, in particular, a humidity detector, such as a hygrometer, to detect the ambient humidity value.

The thermoforming system comprises a database DB configured for storing the at least one start parameter P1 relative to the processing of the article <NUM>, <NUM><NUM>. The database DB is connected to the thermoforming machine <NUM> (<FIG>). The database DB may be connected to the thermoforming machine <NUM> by a cabled connection, or in wireless mode. The database DB may comprise a remote Cloud server connected to the thermoforming machine by an Internet network. In particular, the at least one start parameter P1 comprises at least one product parameter, relating to chemical-physical and/or dimensional properties of the article, and at least one machine parameter, relating to the geometry of one or more components of the thermoforming machine <NUM>.

The product parameter may comprise a material M of the article <NUM>, <NUM>, <NUM>, which may be selected from materials including at least one thermoplastic polymer.

The product parameter may comprise a dimension H1 of the blank product <NUM> to be processed, for example the thickness of the slab to be thermoformed. In a further embodiment, in addition or alternatively to the thickness, the dimension H1 of the blank product <NUM> may comprise a width and/or a length of the slab to be thermoformed.

In addition or alternatively to the material M and/or to the dimension H1, the product parameter P11 may comprise a desired final geometry G3 of the thermoformed product <NUM>, i.e. a shape of the finished product that it is desired to produce by the thermoforming method. The desired final geometry G3 may be defined by a matrix or by one or more vectors containing geometric parameters, for example spatial coordinates of a series of desired positions of points of the desired thermoformed product. The desired final geometry G3 can be stored in an electronic memory, in a three-dimensional drawing document, or solid model, or CAD 3D.

The at least one machine parameter P12 comprises a mould shape G10, i.e. a geometry of the shaped contact surface to imprint the shape thereof on the article <NUM>, <NUM>, <NUM>, in particular on the intermediate product <NUM> to obtain the thermoformed product <NUM>. The mould shape G10 can be defined by a matrix or by one or more vectors containing geometric parameters, for example spatial coordinates of a series of points. The mould shape G10 can be stored in an electronic memory, in a three-dimensional drawing document, or solid model, or CAD 3D.

The database DB can include a finished product database comprising at least two desired final geometries G3 of the thermoformed product <NUM>. The database DB includes at least two mould shapes G10 to imprint on the article <NUM>, <NUM>, <NUM>. In particular, the database DB can comprise hundreds of desired final geometries G3 and hundreds of mould shapes G10.

The database DB can include a blank product database comprising at least two materials M of the article <NUM>, <NUM>, <NUM> and/or at least two dimensions H1 of the blank product <NUM>. In particular, the database DB can comprise hundreds of materials M and/or hundreds of dimensions H1.

The thermoforming system comprises, in particular, a user terminal device <NUM> connected to the database DB and to the thermoforming machine <NUM> and configured to permit an operator of the thermoforming machine <NUM> to select the at least one start parameter P1. The user terminal device <NUM> can be provided with a human machine interface (HMI) that enables the operator to interact both with the documents stored in the database DB and with the thermoforming machine <NUM> (<FIG>). The user terminal device <NUM> can further be configured to display and permit continuous monitoring of the at least one operating parameter P2, of the at least one control parameter P3, of the at least one parameter of actual PR and of the at least one environmental parameter. The user terminal device <NUM> can be connected to the database DB and/or to the thermoforming machine <NUM> by a cabled or wireless connection. The user terminal device <NUM> can comprise a desktop PC and/or wearable devices and/or movable devices.

The thermoforming machine <NUM> comprises control means, which is not illustrated, configured for controlling by the at least one control parameter P3 the plurality of heating elements <NUM> and/or the forming means, as disclosed below. The control means can comprise a programmable logic controller (PLC).

The thermoforming machine <NUM> comprises calculating means, which is not illustrated, configured for: estimating the at least one operating parameter P2 on the basis of the at least one start parameter P1; calculating the at least one control parameter P3 on the basis of the operating parameter P2 and comparing the at least one actual parameter PR detected with the at least one operating parameter; and on the basis of the comparison modifying the at least one control parameter P3. In other words, the calculating means is configured for performing a simulation based on the start parameter P1 that provides as a result an operating parameter P2 and a control parameter P3 and for correcting this result on the basis of at least one incoming actual parameter PR. The calculating means is further configured for modifying further the least one control parameter P3 on the basis of the at least one environmental parameter. The calculating means can comprise a computer, or a laptop, or a similar device provided with a processor (CPU). The at least one operating parameter P2 and the at least one control parameter P3 will be disclosed below in the description. The calculating means is connected in a cabled or wireless manner to the thermoforming machine <NUM>, to the user terminal device and to the database DB.

Such a thermoforming system can implement the thermoforming method disclosed below (<FIG> and <FIG>).

The thermoforming method for controlling the thermoforming machine <NUM> for processing the article <NUM>, <NUM>, <NUM> comprises a setting step of setting the at least one start parameter P1. This setting step can be performed by the operator by selecting the at least one start parameter P1 by the user terminal device <NUM>.

The thermoforming method comprises an estimating step of estimating the at least one operating parameter P2 of the thermoforming method on the basis of the at least one start parameter P1. The at least one operating parameter P2 is an "initial" parameter, i.e. a first setting parameter of the thermoforming method, deriving from a simulation based on a numeric model having as an input variable the at least one start parameter P1.

With reference to <FIG>, the simulation can comprise a structural analysis of the finished elements FEA and/or an analytical geometry analysis AGA performed on structural and/or geometrical parameters of the article <NUM>, <NUM>, <NUM>. Further, the simulation can be further implemented con the application of neural and artificial intelligence AI networks configured for learning from experience and from preceding simulations - stored for example in the database DB - i.e. from preceding operating parameters P2 and/or preceding control parameters P3 obtained with the same and/or similar start parameters P1. The simulation can consider the shaping induced by the mould geometry G10. The results of this simulation are a distribution of the thickness HS of the simulated intermediate product, the respective stretching coefficient SRS and the shape or geometry of the intermediate product <NUM>, i.e. a simulated geometry GS2.

The at least one operating parameter P2 comprises the simulated intermediate geometry GS2 of the intermediate product <NUM> and a respective simulated temperature distribution TS2 applicable to the blank product <NUM> to obtain the simulated intermediate geometry GS2. The simulated geometry GS2 comprises a series of simulated positions of respective points of the simulated intermediate product. In other words, the step of estimating comprises predicting the simulated temperature TS2 distribution that has to be reached on the blank product <NUM> to obtain the intermediate product <NUM> starting from the at least one start parameter P1.

The simulated temperature TS2 distribution comprises at least one simulated temperature value associated with the area of the blank product <NUM> and/or of the intermediate product <NUM>. In particular, the simulated temperature TS2 distribution comprises a thermal matrix of simulated local temperatures, each element of this thermal matrix carries information on the temperature that the specific area of the blank product <NUM> and/or of the intermediate product <NUM> has to reach.

The thermoforming method comprises a calculating step of calculating the at least one control parameter P3 to control the thermoforming machine <NUM> on the basis of the at least one operating parameter P2.

In particular, the at least one control parameter P3 is used to control the plurality of heating elements <NUM> and the forming means.

The thermoforming method comprises a detecting step of detecting at least one actual parameter PR of the thermoforming method and a comparing step of comparing the at least one actual parameter PR with the at least one operating parameter P2. On the basis of the comparing step, a modifying step of modifying the at least one control parameter P3 is performed. The detecting, comparing and modifying steps are in a cyclical sequence. In other words, these steps are repeated one after another in the described order. These steps are conducted in particular continuously.

In other words, in a start step of starting the thermoforming machine <NUM>, the at least one control parameter P3 is based on the at least one operating parameter P2, thus on parameters deriving from the simulation; after the start step, continuous monitoring starts on the thermoforming method (in particular, the step of detecting the at least one actual parameter PR) and a feedback operating mode in which the control parameter P3 is corrected on the basis of an actual/detected parameter measured on the article <NUM>, <NUM>, <NUM>, i.e. on the basis of the at least one actual parameter PR.

The thermoforming method comprises a heating step of heating the article <NUM>, <NUM>, <NUM> (<FIG>). The heating step is used to soften the article <NUM>, <NUM>, <NUM>, in particular the blank product <NUM>, to set up the article <NUM>, <NUM>, <NUM> for a subsequent moulding step. The moulding step comprises the pressure shaping step and/or the step of shaping under vacuum.

The at least one control parameter P3 comprises at least one thermal power value PT to be supplied to the area of the article <NUM>, <NUM>, <NUM> and/or a heating time TPT. The heating time TPT is the time period in which the thermal power PT is supplied on the area of the article <NUM>, <NUM>, <NUM>. The thermal power value PT and/or the heating time TPT can control the plurality of heating elements <NUM>. A respective thermal power value PT and/or a respective heating time TPT is associated with each heating element <NUM>. In the heating step, the thermal power value PT and/or the heating time TPT are modified on the basis of the at least one actual temperature TR detected on the area of the article <NUM>, <NUM>, <NUM>. In particular, the thermal power value PT is compared by a law that links the thermal power to be supplied to the temperature of the article <NUM>, <NUM>, <NUM>, to the at least one actual temperature value TR.

The pressure shaping step for pressure shaping the article <NUM>, <NUM>, <NUM> is performed by supplying onto the article <NUM>, <NUM>, <NUM> a pressurized fluid (<FIG>). The pressure shaping step is used to give the article <NUM>, <NUM>, <NUM>, a suitable shape, in particular a concave shape, upon insertion of the mould so as to even out the distribution of the stresses and/or the thickness in the article <NUM>, <NUM>, <NUM>. As mentioned, in the pressure shaping step the intermediate product <NUM> is obtained. The pressure shaping step is thus subsequent to the heating step.

The at least one control parameter P3 comprises at least one fluid flow rate value QF to be supplied to the article <NUM>, <NUM>, <NUM> and/or a supplying time TQF and/or a fluid pressure PF. The supplying time TQF is the time period in which the fluid flowrate is supplied onto the article <NUM>, <NUM>, <NUM>. The fluid flow rate value QF and/or the supplying time TQF and/or the fluid pressure PF can control the fluid supplying means. In the pressure shaping step, the fluid flow rate value QF and/or the supplying time TQF and/or the fluid pressure PF can be modified on the basis of the actual position X of the point of the article <NUM>, <NUM>, <NUM>. In the pressure shaping step, the actual position X detected on the article <NUM>, <NUM>, <NUM> is compared with the respective simulated position contained in the simulated intermediate geometry GS2.

The step of shaping under vacuum the article <NUM>, <NUM>, <NUM> is performed by making the article <NUM>, <NUM>, <NUM> adhere to the contact surface of the forming mould (<FIG>).

The step of shaping under vacuum is used to confer on the article <NUM>, <NUM>, <NUM> the finished shape of the thermoformed product <NUM>. In the specific embodiment, the step of shaping under vacuum is performed on the intermediate product <NUM> and is thus subsequent to the pressure shaping step.

The at least one control parameter P3 comprises at least one vacuum value to be applied to the article <NUM>, <NUM>, <NUM> and/or a vacuum time. The vacuum time is the time period in which the vacuum on the article <NUM>, <NUM>, <NUM> is generated. The vacuum value and/or the vacuum time can control the suction means. In the pressure shaping step, the vacuum value and/or the vacuum time can be modified on the basis of the at least one actual position X of the point of the article <NUM>, <NUM>, <NUM>. In the step of shaping under vacuum, the actual position X detected on the article <NUM>, <NUM>, <NUM> is compared with the respective desired position contained in the desired final geometry G3.

The thermoforming method comprises a detecting step of detecting at least one environmental parameter in the work environment W where the thermoforming machine <NUM> is located.

On the basis of the at least one environmental parameter, a step is provided of further modifying the at least one control parameter P3. This enables during processing, the environmental conditions of the work environment W to be taken into account, which can differ on the basis of the climatic zone in which the thermoforming machine <NUM> is installed and/or the time of year and/or during the solar day and/or other energy variables relating to the work environment W.

The step of further modifying the at least one control parameter P3 on the basis of the at least one environmental parameter can precede the step of detecting the actual parameter PR. In particular, the ambient temperature value and/or the ambient humidity value can be used to set the thermal detecting means, in particular in the case of infrared thermal detecting means for correcting or setting an actual temperature value detected on the blank product <NUM> before being heated. Alternatively, the step of further modifying the at least one control parameter P3 can be run during one of the detecting, comparing and modifying steps.

In particular, the ambient humidity value can be used to correct a thermal power value PT (and/or a heating time TPT) taking account of the heat exchange between the plurality of heating elements <NUM> and the air that surrounds the article <NUM>, <NUM>, <NUM> to be heated.

Additionally or alternatively to the step of further modifying the at least one control parameter P3 on the basis of the at least one environmental parameter, the aforesaid step of estimating the at least one operating parameter P2 on the basis of the at least one start parameter P1 can further comprise modifying the at least one operating parameter P2 on the basis of the at least one environmental parameter. In other words, the simulation can have as input parameters the ambient humidity value and the ambient temperature value for estimating with greater precision - with respect to the step of estimating the at least one operating parameter P2 on the basis of the at least one start parameter P1 - the distribution of intermediate temperatures TS2 (and the respective simulated intermediate geometry GS2).

It should be noted how, by applying the thermoforming method according to the invention, it is not necessary to dispose of expert personnel to minimize the production time of the thermoformed product.

Owing to the detection of the actual parameters of the thermoforming method, and the implementation with the simulation/estimate of the initial operating parameters the optimum process conditions can be reached in a short time.

Further, implementing the simulation and feedback control enables the quality of production to be maintained virtually constant, ensuring at the same time the reproducibility of the process parameters.

Further, considering environmental variables as input variables to calculate the control parameters of the thermoforming method permits great flexibility of the thermoforming machine in any work environment, reducing the time of installation and setting of the thermoforming machine.

Claim 1:
Thermoforming method for controlling a thermoforming machine (<NUM>) for processing an article (<NUM>, <NUM>, <NUM>) in thermoplastic material, said method comprising:
a. setting at least one start parameter (P1), said at least one start parameter (P1) comprising at least one parameter which is related to processing said article (<NUM>, <NUM>, <NUM>), wherein said article (<NUM>, <NUM>, <NUM>) comprises a blank product (<NUM>) and/or an intermediate product (<NUM>) and/or a thermoformed product (<NUM>);
b. estimating at least one operative parameter (P2) of said thermoforming method based on said at least one start parameter (P1);
c. calculating at least one control parameter (P3) for controlling said thermoforming machine (<NUM>) based on said at least one operative parameter (P2);
d. detecting at least one actual parameter (PR) of said thermoforming method;
e. comparing said at least one actual parameter (PR) which has been detected with said at least one operative parameter (P2) which has been estimated;
f. based on said comparing, modifying said at least one control parameter (P3);
wherein said detecting, said comparing and said modifying are in a cyclical sequence;
characterized in that said at least one start parameter (P1) comprises at least one machine parameter and said at least one machine parameter comprises a mould shape (G10) to imprint on said intermediate product (<NUM>).