RELATED APPLICATIONS

This application is a § 371 National Phase Application of International Application No. PCT/EP2015/077668, filed on Nov. 25, 2015, which claims priority to German Application No. 10 2014 117 332.5, filed on Nov. 26, 2014, both of which are incorporated herein by reference in their entirety.

The present invention relates to a method of controlling a step of a process automatically carried out by a machine and a method of producing a particle foam part.

Particle foam parts based on thermoplastic polyurethane are known from WO 94/20568. These particle-foam parts are made from expandable particle-shaped thermoplastic polyurethanes. For molded part production, the pre-expanded, where applicable pressure-charged thermoplastic polyurethane particles are placed in a heatable mold, and heated sufficiently for the particles to become welded together. The heating is effected through the application of steam. If necessary, the particles may be pressure-charged before molded part production. After demolding, the part should be conditioned until it has reached a constant weight. Conditioning takes place at temperatures of 20-120° C. The thermoplastic polyurethane particles may be provided with a blowing agent, such as, for example, butane or CO2. Solid blowing agents may also be used, which split off gas under heating, such as azocarbonamide or toluene-p-sulphonic acid hydracite.

Known from WO 2014/011537 A1 is a method for the production of shoe soles from thermoplastic polyurethane foam particles. Other methods of producing particle-foam parts are disclosed in DE 1 243 123 A, DE 1 704 984 A, U.S. Pat. Nos. 4,822,542 and 6,220,842 B1.

The advantage of particle-foam parts made of particles based on thermoplastic polyurethane (TPU particles) lies in their high elasticity in comparison with particle-foam parts based on other plastics, in particular polystyrol and polypropylene.

Great efforts have therefore been made to make such particle-foam parts based on polyurethane accessible to mass production. In particular such particle foams based on polyurethane are, because of their mechanical properties, of very great interest for shoe soles.

The manufacture of soles for shoes from foamed particles of thermoplastic polyurethane is also disclosed in WO 2012/065926 A1. Here the foamed polyurethane particles are embedded in a matrix material made of polyurethane foam, thus creating a hybrid material. Because of the properties of the foamed polyurethane particles, the soles have good damping properties, may be bent with minimal force, and have high rebound resilience.

Described in WO 2013/013784 A1 is a further method for the manufacture of a sole or a part of a sole of a shoe, in which the sole is made of foamed thermoplastic polyurethane based on urethane (TPU, E-TPU, TPE-U) and/or on the basis of polyether-block-amide (PEBA). The foam particles are preferably linked by a binder. As binder, a two-component polyurethane system is used.

Disclosed in WO 2010/010010 A1 are expandable thermoplastic polymer blends containing a blowing agent, also thermoplastic polyurethane (TPU) and styrene polymer. The preferred percentages by weight of thermoplastic polyurethane lie between 5 and 95 and the percentages by weight of styrene polymer between 5 and 95, with the percentages by weight of thermoplastic polyurethane and styrene polymer adding up to 100 parts. The polymer blend may contain a further thermoplastic polymer.

Known from WO 2013/182555 A1 is a method of producing a particle-foam part from thermoplastic polyurethane particles, in which the foam particles are wetted in water containing lubricant for conveyance in a gas flow. This is intended to prevent the particles from sticking together during movement. The foam particles are sprayed with water by nozzles.

Described in WO 2014/128214 A1 is a method and an apparatus for the production of a particle foam part in which the foam particles are fed from a material container by means of a pipe to a mold, wherein steam is added to the foam particles to be supplied.

DE 196 37 349 A1 discloses an apparatus for the sintering of foamable plastic material. The plastic material used is pre-expanded polystyrol, which is fed from a supply tank to a sinter chamber. A sinter chamber is surrounded by several steam chambers. Using sensors, the temperature at the sinter chamber prevailing in the area of each individual steam chamber, the foaming pressure prevailing there, and the steam pressure in the sinter chamber are detected and passed on to a controller. The temperature, foaming pressure and steam pressure of each individual steam chamber should here be so controlled that, on reaching a target value, this target value should be held constant within relatively narrow limits, by suitable variation of the steam supply to the associated steam chamber. If all steam chambers have reached their target values for temperature and for steam pressure, or if a maximum time has elapsed, then the steam chambers are cooled so that the foamed plastic part solidifies.

Described in EP 224 103 B1 is an adaptive control process for the foaming and sintering of plastic bodies made of pre-expanded plastic material. The sintering apparatus has a sinter chamber which is surrounded by two steam chambers, to which it is connected by a multiplicity of nozzles. The sintering apparatus is provided with a multiplicity of pressure and temperature sensors in the area of the flow passages, the steam chambers, the steam generator and a vacuum generator. In addition, the plastic parts produced in the sintering process may be fed to a quality measurement process. The quality parameters are molding accuracy, moisture content, bending strength and surface roughness or strength. With the aid of the quality parameters and the process of statistical variation of the control criteria, these factors may be set automatically at the optimum level.

DE 32 43 632 A1 relates to a method and an apparatus for the sintering of particle foam bodies. With this method it should be possible to produce different moldings from diverse foamable plastics. Since the materials on delivery are subject to considerable tolerances, differing e.g. in moisture and blowing gas content depending on pre-foaming and interim storage, characteristic values are determined during processing from measured temperature and pressure values. These are used for ongoing determination of default values or for their correction. The characteristic values and the new default values are at the same time compared with preset material-specific limit values and/or mean values, and overshoots or deviations are passed on to the material supply as an alarm or control signal. This should make it possible for the operating control system to compensate for tolerances in material properties, also fluctuations in the states of other media supplied and the different states of the mold in start-up and continuous operation, so that moldings with largely identical molded part properties are obtained. The preset characteristic values correspond to a specific density, strength, maximum moisture content and accuracy of shape. The process time, moreover, should not be unnecessarily extended and energy consumption not increased by an extreme amount. Measuring devices are provided for detecting molded part properties of the finished moldings, with this measured data serving for feedback and comparison with the preset molded part properties. From the comparison of results, a correction of the process operation is made, to the extent that unacceptable deviations occur. In this way the process is self-optimized.

In an apparatus known from EP 192 054 B, a softening point of the plastic is determined from a pressure and temperature curve in the sinter chamber. From this softening point and an associated sintering pressure or sintering temperature, a maximum demolding temperature is determined, below which the plastic part may be removed from the mold. This makes possible an especially rapid process sequence.

EP 1 813 408 A1 discloses a method for the filling of molds with expanded polymer particles. Here it is provided that a filling device or a feed for a particle-carrier gas mixture attached to it is provided with at least one measuring device for the flow direction or the temperature of a polymer-particle-carrier gas mixture. The measuring device may be a flow sensor or a temperature sensor. The measuring device may also be connected to an automatic controller in such a way that, depending on the signal received from the measuring device, the supply of particle-carrier gas mixture and where applicable steam is interrupted and where applicable an injector gas feed for rinsing the pipes is opened. In addition, the filling device is able to terminate supply of the polymer-particle-carrier gas mixture as soon as the measuring devices indicate that the mold is filled with polymer particles.

Described in DE 35 41 258 C1 is an adaptive control method for the foaming and sintering of plastic. A sintering apparatus for carrying out this adaptive control method is said to have several sensors for various parameters. According to this method it is provided that the injection molding process is terminated when a pressure measured value at an injector pressure sensor has risen by a preset value as compared with a pressure measured value measured shortly before the start of injecting. Heating should be terminated when condensate temperatures at temperature sensors lie above a preset condensate temperature. Cross steaming should be terminated when a differential pressure has reached a specific preset value. Sintering should be terminated when the differential pressure during the sintering period has exceeded a maximum or a specific preset value or a chamber pressure has exceeded a specific value, after which a predetermined time has elapsed. Consequently, with this method, two different control criteria are critical, namely the pressure criterion and a time criterion. According to an alternative embodiment, the end of the sintering phase may also be determined from a differential temperature, followed by a waiting time based on a time criterion. It should also be possible though this maximum to obtain a specific sintering state largely irrespective of the molding of the material used. Consequently, probably all phase times are limited by suitable preset maximum times so that e.g., in the case of a sensor failing, the process still continues.

JP 2001-341 149 A1 discloses a method for the molding of resin. According to this method it is provided that the mold pressure of the particles during foaming, when heated up, and a steam pressure, are detected in such a way that the detected values correspond to the previously defined optimal foam pressure curve. This is realized by means of suitable pressure sensors mounted in an ejector pin.

The invention is based on the problem of controlling a step of a method executed automatically by a machine in such a way that the step is optimally controlled in respect of the efficiency and also the precision of the method.

A further problem of the invention is to control a step of a production process implemented automatically by a machine in such a way that the step may be executed optimally in respect of the efficiency of the production process and also the quality of a product to be made by the production process.

A further problem of the present invention is to create a method for the production of a particle foam part, by which a very efficient production of the particle foam parts is obtained.

A further problem of the present invention is to create a method and an apparatus for the production of a particle foam part, by which particle foam parts of high quality may be produced.

A further problem of the present invention is to create a method and an apparatus for the production of a particle foam part, by which particle foam parts of different size and/or different shape may be produced reliably.

A further problem of the present invention is to create a method and an apparatus for the production of a particle foam part which eliminates one or more of the disadvantages of the prior art.

One or more of the problems is or are solved by a method according to the independent claims. Advantageous developments are set out in the relevant dependent claims.

The method of controlling a step of a process automatically carried out by a machine is characterized in that a sensor is used to measure for a step a characteristic variable which has an exponential course and, with the aid of several consecutive measurements of the characteristic variable, the time constant of the exponential variation is determined, and the step is terminated after it has been implemented for a period of time corresponding to a predetermined multiple of the time constant.

In the method according to the invention, a step of a process is controlled with the aid of a characteristic variable. The characteristic variable describes an important state of the machine, a product to be produced or worked by the machine, or a physical state to be influenced by the machine, wherein the characteristic variable correlates in particular with a final state which is to be achieved by execution of the step. The characteristic variable also has the property of varying exponentially during the process. The variation of the characteristic variable can often be very different. If the characteristic variable is a temperature, then its pattern may depend for example on the room temperature of the room in which the machine is located. It can also depend on the nature and the quality of materials to be processed.

The course of change of the characteristic variable may also depend for example on the volume of a product to be produced.

The inventors of the present invention have recognized that, by determining the time constant of an exponential change in the characteristic variable, the duration of a step to be executed automatically by a machine may be set individually in such a way that the target condition is always correctly maintained. By this means the step is executed optimally in respect of the result to be obtained hereby. On the other hand, by using the time constant to set the duration of the step, the step itself is executed only for as long as necessary. This means that the duration is set so that the desired objective is achieved, but not longer. In this way, the step is executed efficiently in terms of time. The operating time of a machine causes costs to be incurred. These costs are minimized through the efficient execution of the step in time. The whole process is hereby optimized for time.

The method may include a casting process with the following steps:

filling of the mold cavity with a material to be solidified

cooling of the mold cavity (stabilization step)

demolding of the mold cavity.

During the stabilization step, the mold cavity and/or the part body may be cooled, for example by feeding cooling water or cooling air into the cooling passages formed in the mold.

The characteristic variable of the stabilization step may be the temperature in the mold cavity or the temperature of the mold.

The process may be a production process for the production of a specific product. The process may however also be a machining process for modifying an already existing product and bringing it into a desired state, using a machine.

The process may for example also be the air conditioning of a room, such as for example the passenger compartment of a motor vehicle. The air conditioning of the passenger compartment of a motor vehicle is extremely complex and depends on many parameters (solar radiation, available waste heat of an internal combustion engine, etc.). On the other hand, one would like to set as quickly as possible a certain target temperature in the motor vehicle, without causing any excessive variations in the process. As characteristic variable, a temperature in the passenger compartment is detected, which may involve one or more sensors.

The flow rate of a conditioned airflow into the passenger compartment is controlled on the basis of the variation of the temperature of the passenger compartment.

The method may be provided for the production of particle foam parts, comprising the following steps:

filling of a mold cavity with foam particles

welding of the foam particles to form a particle foam part

demolding of the mold cavity, wherein the mold cavity is opened and the particle foam part removed.

According to one aspect, the invention is characterized in that a sensor is used to measure a variable which is characteristic for a step or a sub-step. This variable has an exponential course wherein, with the aid of several consecutive measurements of the characteristic variable, the time constant of the exponential variations is determined and the step is ended after implementation for a period of time corresponding to a predetermined multiple of the time constant.

With this method, therefore, the period of time for which the step or sub-step of the method is conducted is determined individually. This invention is based on the finding that a characteristic variable which varies according to an exponential pattern, first of all varies strongly and then gradually approaches a target or final state. After a certain multiple of the sub-step it is ensured that the characteristic variable has approached a certain low percentage portion of the target value. The target value is the value which the characteristic variable would assume if the step were carried out for an indefinite time. The target value may therefore also be described as the final state.

FIG. 5shows three exponential falling curves I, II and III wherein for these three curves, according to the formula given above, K=1 and C=0, for which reason the initial state is 1 and the final state is 0. Curve I has a time constant T of 1 s, curve II a time constant T of 2 s, and curve 3 a time constant T of 3 s. The time in seconds is plotted on the abscissa and the ordinate shows any desired measured variable. All three curves thus begin at time point 0 with value 1. After 3T the value is in each case 0.05, i.e. it has reduced by 95% and is now only 5% from the final state, which is here 0.

This step or sub-step of the method is conducted until the characteristic variable is sufficiently close to the target value. In this way it is ensured that this step or sub-step is achieved to an adequate extent. On the other hand, this step or sub-step is executed no longer than the period of time which corresponds to the predetermined multiple of the time constants, so that this step or sub-step is not drawn out unnecessarily. By this means, as compared to conventional methods in which the duration of a step or sub-step is set at a fixed value, considerable time is saved and the entire process is made more efficient.

A further benefit of this method is that the target value need not be set explicitly. This follows automatically from the fact that the characteristic variable changes with an exponential pattern. It is therefore unnecessary, on setting up the system, to specify a target value in advance.

A further benefit of this method lies in the fact that, with certain steps or sub-steps of the method, certain properties of the material to be processed vary, with this variation of properties depending on the duration for which this step or sub-step is applied. As an example of this method, the control of a cross steaming operation, in which steam consumption is used as characteristic variable, is described below. In the course of cross steaming, on account of the increasing welding of the foam particles, permeability or porosity increases with increasing duration of the cross steaming process. Through the control of cross steaming duration by determining the time constant of steam consumption it is ensured that, at the end of the cross steaming step, porosity or permeability of the particle foam part is always the same. In this way and with this method, the production of foam particle parts of varying size or varying thickness may be controlled automatically without the need to determine and set duration on an individual basis. Consequently, in one machine, the mold may be interchanged for different particle foam parts, without the need for manual adjustment of the duration of the process step of cross steaming, while particle foam parts of consistent quality are obtained.

Typically the predetermined multiple of the time constants lies at around two to four times.

The pressure and/or the temperature in the mold cavity may be used as characteristic variable. This applies in particular to welding, with the sub-steps autoclaving, secondary steaming (optional), cooling and stabilization. In addition, steam consumption may be used as characteristic variable for cross steaming.

An exponential course of characteristic variable G is described by the following formula:

G=K·et0-tτ+C,

in which t stands for time, t0for start time, K for a constant, C for a further constant and T is the time constant. The initial state is K+C and the final state is C. K may be both positive and negative, so that G may approach the final state C from above or from below.

The time constant T may be determined with the aid of at least three values of G measured at different times t. Time constant T may be determined using the Levenberg-Marquardt algorithm.

In addition, the foam particles may be subjected to pressure-charging in a supply tank. This means that the gas pressure in the supply tank in which the foam particles are held is increased. By this means, the foam particles are initially compressed. The gas diffuses in the foam particles, which are also described as beads, so that the foam particles expand once again. This expansion is measured. Measurement of the expansion may be ascertained from the filling state of the supply tank. This is therefore a suitable variable to describe the average size of the foam particles. This average size of the foam particles may be used as characteristic variable, with the pressure-charging being terminated for example after two to four times the time constant. By using as characteristic variable a variable suitable for describing the average size of the foam particles it is possible to subject any desired amount of foam particles to pressure-charging, without the need for any manual intervention.

During stabilization, the mold and/or the particle foam bodies are cooled.

The cross steaming is a sub-step of welding in which steam is fed to the foam particles. Here the steam is introduced at one side of the mold and removed at the other side so that air to be found in spandrels between the foam particles is displaced from the mold. For cross steaming, the pressure or the temperature in the mold cavity may also be used as characteristic variable.

According to a further aspect of the present invention, the method for the production of particle foam parts is characterized in that the foam particles are drawn intermittently from a material container.

Due to the intermittent withdrawal of foam particles, bridges between the foam particles which have formed in the material container are broken up and the foam particles separated. This method is especially advantageous for foam particles with an adhesive surface, e.g. eTPU foam particles.

For the intermittent withdrawal of foam particles from the material container, an orifice of the material container may be opened and closed consecutively and/or the air for conveying the foam particles in the pipe may be supplied intermittently.

According to a further aspect of the present invention, a method for the production of particle foam parts is provided in which, at the start of feeding steam into the mold, the mold parts

are spaced a short distance apart (crack gap) and then the two mold parts are moved together, causing the foam particles to be compressed. This method is characterized in that two mold parts are used which, even when spaced apart, are sealed relative to one another. Since the mold, even in the presence of a crack gap, has a substantially gastight seal at its periphery, the air in the spandrels between the foam particles is very efficiently forced through the steam. Since the mold is set with a crack gap, the spandrels are relative large, so that the flow resistance is low and a much faster displacement of air is obtained than would be the case with a completely closed mold. Due to the sealing at the peripheral circumference, the steam does not escape at the side of the mold, but instead flows from one side of the mold to the other side (cross steaming), ensuring that the air is forced out of all the spandrels.

According to a further aspect of the present invention, a method for the production of particle foam parts is provided, which is characterized in that, within a cycle at regular intervals, measured parameters such as temperature and/or pressure in the mold cavity, temperature of a mold bounding the mold cavity, pressure and/or temperature and/or flow volume of steam or condensate supplied or removed, valve positions, flow volume of the compressed air used in filling, are recorded and, with the aid of the recorded measured parameters, one or more predetermined setting parameters are set within the same cycle.

It is true that, in conventional methods for the production of particle foam parts, a multiplicity of measured parameters has in the past been recorded. However, it has been assumed that it is sufficient to record the individual measured parameters once per cycle or a few times per cycle. This is also correct, so long as a multiplicity of identical particle foam parts is being produced. This applies especially if the material used is expanded polystyrol (ePS), expanded polypropylene (ePP) or expanded polyethylene (ePE) which, in comparison with expanded polyurethane are much more easily processed. If, however, it is desired to produce particle foam parts of differing size either in parallel with different molds or sequentially, and in this connection in particular polyurethane-based foam particles are used, then the processes are often unstable. Through the recording of a multiplicity of measured parameters at regular intervals, the process may be controlled much more precisely and reaction can be made within a cycle so that, with this data, distinctly greater flexibility in respect of the shape and size of the particle foam parts and also in respect of the material to be used is obtained. The measured parameters are preferably recorded at intervals of no longer than 10 s and in particular no longer than 5 s or no longer than 2 s. An example of a reaction within a cycle with the aid of several measured parameters measured in the cycle is the determination of the time constant described above. In determining the dissipation over time of the foam pressure in order to terminate secondary steaming, when the variation of foam pressure falls below a predetermined value, represents a reaction within a cycle which requires several measured values within this cycle. A further example of a reaction within a cycle is the automatic termination of cooling when the foam pressure falls below a predetermined threshold and is roughly constant, or the second dissipation of the foam pressure has overshot a zero point and the first dissipation lies below a threshold.

With this method, especially, the duration of the individual steps is set automatically.

According to a further aspect of the present invention, a method for the production of particle foam parts is provided in which one or more measured parameters of the demolded particle foam part are measured and, with the aid of the recorded measured parameters, one or more predetermined setting parameters are set.

By this means, therefore, an automatic feedback into the production process of the measured parameters recorded for the finished particle foam part is created. This ensures that the foam particle parts are produced with consistent quality, making the process substantially more stable.

The measured parameters measured for the demolded particle foam part are e.g., the measured parameters describing surface, in particular measured parameters by which imperfections in the particle foam part may be detected. Other parameters detectable on the demolded particle foam part are weight, size, strength and porosity.

With these measured parameters detected on the demolded particle foam part, preferably the duration of individual steps or sub-steps of the production process and/or a predetermined pressure and/or a prescribed temperature are set automatically.

If the detectable parameter on the demolded particle foam part is its weight, then preferably depending on the weight, the width of a crack gap in filling the mold cavity with foam particles to produce a further particle foam part is set on the basis of the measured weight. If the measured weight is greater than a target weight, then the crack gap is correspondingly reduced and if the measured weight is less than the target weight, then the crack gap is correspondingly enlarged. By setting the crack gap, the amount of foam particles fed to the mold cavity may be adjusted.

This is preferably of advantage in using polyurethane-based foam particles, since here even a slight deviation in quantity from a target quantity of foam particles may lead to considerable differences in quality.

In addition, a geometrical shape may be detected as a measured parameter of demolded particle foam parts. In particular, the course of a specific surface or edge may be considered as such a geometrical shape. The surface has a certain desired pattern, which may be concave, flat or convex in shape, or may have corresponding different sections. If the measured geometrical shape is more convex than a specified shape, then the individual foam particles have been too strongly expanded. The expansion of the foam particles may be influenced by the duration of stabilization, autoclaving and/or cooling. If too much expansion is detected through the measured geometrical shape, then the stabilization and/or autoclaving should be shortened or the cooling lengthened.

In filling, in the method described above, foam particles are conveyed into the mold cavity via a conveyor line using compressed air, with the conveyor line being blown free after the mold cavity has been filled completely.

Welding of the foam particles comprises preferably the following steps: rinsing of steam chambers

cross steaming of the mold cavity, wherein the cross steaming may be divided into at least two sub-steps, in which the steam is passed through the mold cavity in opposite directions (=first cross steaming and second cross steaming)

autoclaving of the foam particles, in which they are subjected to steam. In addition, welding of the foam particles may include secondary steaming (optional), cooling of the mold and of the particle foam part, stabilization (optional).

At the end of welding and before demolding of the particle foam part, the latter may be stabilized by means of

spraying cooling water into the mold cavity and/or

applying a partial vacuum to the mold cavity and/or

temporarily compressing the particle foam part using compressed air and/or

keeping the particle foam part in the mold cavity for a predetermined period of time.

Stabilization ensures that the walls of the foam particles of the particle foam part do not undergo plastic deformation, or else only slightly, during demolding. Through stabilization, the pressure within the foam particles is reduced sufficiently that it no longer significantly expands the foam particles during release of the particle foam part from the mold halves of the mold.

Preferably after demolding, a mold bounding the mold cavity and/or a quill located in a filling injector are cleaned by passing compressed air through them.

According to a further aspect of the present invention, a method for the production of particle foam parts is provided which is characterized in that a mold with a heating device and bounding the mold cavity is set at a predetermined temperature between each cyclical repetition of the production process.

Because of the conditioning of the mold by means of a heating device it is not necessary to condition the mold using steam, so that the step of rinsing the steam chambers is shortened and the efficiency of the process may thereby be enhanced. Moreover, the temperature of the mold may be set more quickly and more precisely and in particular at a higher temperature so that, on steaming the foam particles in the mold cavity, little heat is drawn from the steam as it enters the mold cavity, and a better heat input is obtained.

According to a further aspect of the present invention, a method for the production of particle foam parts is provided in which, after welding of the foam particles and before demolding of the particle foam part, a process medium such as e.g. compressed air or steam is fed through the mold cavity and the flow volume is measured so that, with the aid of the flow volume, the porosity of the workpiece may be determined. The measured porosity is a measured parameter which may be used for monitoring quality and for control of the production process. This porosity may be determined with the aid of the measured parameter of steam flow. The measurement of steam flow is, however, of basic interest, and may also be made during other process steps. The measurement of steam flow is effected preferably by determining a steam pressure and a steam temperature at the inlet valve of a steam chamber adjoining the mold cavity, and the steam flow, the steam temperature and a condensate amount at an outlet valve of another steam chamber adjacent to the mold cavity. The steam flow may be calculated from these measured parameters.

Several aspects of the present invention are explained above. These different aspects may be used separately or in any desired combination with one another.

