Patent Description:
Injection molding is a technology commonly used for high-volume manufacturing of parts constructed of thermoplastic materials. During repetitive injection molding processes, a thermoplastic resin, typically in the form of small pellets or beads, is introduced into an injection molding machine which melts the pellets under heat and pressure. In an injection cycle, the molten material is forcefully injected into a mold cavity having a particular desired cavity shape. The injected plastic is held under pressure in the mold cavity and is subsequently cooled and removed as a solidified part having a shape closely resembling the cavity shape of the mold. A single mold may have any number of individual cavities which can be connected to a flow channel by a gate that directs the flow of the molten resin into the cavity. A typical injection molding procedure generally includes four basic operations: (<NUM>) heating the plastic in the injection molding machine to allow the plastic to flow under pressure; (<NUM>) injecting the melted plastic into a mold cavity or cavities defined between two mold halves that have been closed; (<NUM>) allowing the plastic to cool and harden in the cavity or cavities while under pressure; and (<NUM>) opening the mold halves and ejecting the part from the mold. Upon ejecting the part from the mold, the device that injects the melted plastic into the mold cavity or cavities (e.g., a screw or an auger) enters a recovery phase in which it returns to an original position.

In these systems, a control system controls the injection molding process according to an injection cycle that defines a series of control values for the various components of the injection molding machine. For example, the injection cycle can be driven by a fixed and/or a variable melt pressure profile wherein the controller uses (for example) sensed pressures at a nozzle as the input for determining a driving force applied to the material. The injection cycle may also be controlled by a fixed or variable screw velocity profile wherein the control senses the velocity of the injection screw as input for determining the driving speed applied to the material.

Changes in molding conditions can significantly affect properties of the molten plastic material. As an example, material specification differences between resin batches and changes in environmental conditions (such as changes in ambient temperature or humidity) can raise or lower the viscosity of the molten plastic material. When viscosity of the molten plastic material changes, quality of the molded part may be adversely impacted. For example, if the viscosity of the molten plastic material increases, the molded part may be "under-packed" or less dense, due to a higher required pressure, after filling, to achieve optimal part quality. Conversely, if the viscosity of the molten plastic material decreases, the molded part may experience flashing as the thinner molten plastic material is pressed into the seam of the mold cavity. Furthermore, recycled plastic material that is mixed with virgin material may impact the melt flow index (MFI) of the combined plastic material. Inconsistent mixing of the two materials may also create MFI variation between cycles.

Some conventional injection molding machines do not adjust the molding cycle to account for changes in viscosity, MFI, or other material properties. As a result, these injection molding machines may produce lower quality parts, which must be removed during quality-control inspections, thereby leading to operational inefficiencies. Some systems may account for changes in material viscosities by sensing a mold characteristic (e.g., a cavity pressure measurement) and reacting to the characteristic. For example, if the viscosity of the material increases, the cavity pressure measurement will be delayed, and thus the system will react upon sensing this delay. Conversely, if the viscosity of the material decreases, the cavity pressure measurement will occur earlier, and thus the system will react upon this earlier measurement. In other systems, a driving pressure may be adjusted in order to normalize a time required to measure an initial cavity pressure value, thereby compensating for viscosity changes that may occur in the material. However, these systems are still reactionary to the oftentimes variable incoming viscosity of the material.

<CIT> recites a control for an injection molding machine measuring the viscosity characteristics of the plasticized material by monitoring pressure in the melt stream being injected at a predetermined position of the forward stroke of the ram during flow of the material into the mold.

<CIT> recites a controller of the injection unit arranged to continuously rotate the screw during both conventional plasticizing operation and shot injection. In this way the RS unit is more efficient, utilizing less energy and producing greater resin output. The injection unit includes a non-return valve adjacent a nozzle, which non-return valve is either configured to rotate with the screw to reduce wear or presented as a ball check style noon-return valve.

<CIT> recites an injection screw rotated at a set speed and retreated by performing back pressure control for keeping a resin pressure at a set pressure. When the retreat position of the screw reaches a change point set nearby a set metering completion position, the back pressure control for keeping the resin pressure at a set resin pressure is stopped and a command for positioning the screw at a metering completion position is output to position the screw at the metering completion position.

While the invention is defined in the independent claims, further aspects of the invention are set forth in the dependent claims, the drawings and the following description.

Embodiments within the scope of the present invention are directed to the control of injection molding machines to produce repeatably consistent parts by using machine parameters and measurements to ensure the molten plastic material being ejected maintains a desired viscosity (and/or density) value and/or falls within a specified allowable range of viscosity (and/or density) values. Systems and approaches for controlling the injection molding machine include injecting a molten polymer into the mold cavity according to the injection cycle using a screw that moves from a first position to a second position. Upon completion of the injection cycle, a recovery profile commences where the screw is moved to the first position. Using a sensor, at least one variable is measured during the recovery profile. At least one operational parameter of the injection molding machine is adjusted based on the at least one measured variable during the recovery profile. In some forms, a target variable recovery profile may be first created and relied upon during commencement of the recovery profile.

In these examples, the at least one operational parameter may be in the form of at least one of a back pressure value or a screw rotational speed. The at least one variable may be in the form of a pressure (e.g., a backpressure) value of molten polymer being urged towards a nozzle of the screw. In some forms, the sensor is located at a leading end of the screw near the nozzle. The sensor may alternatively be located at any position ahead of a check ring of the screw.

In some approaches, the at least one variable may be in the form of a nozzle pressure. The operational parameter may be in the form of an adjustable back pressure having a plurality of discrete set points. The back pressure is adjusted according to the sensed nozzle pressure. In other approaches, the operational parameter may be in the form of a continuously variable back pressure that is adjusted according to the sensed nozzle pressure.

In accordance with another aspect, an injection molding machine may include an injection unit having a mold forming a mold cavity and a screw that moves from a first position to a second position, a controller adapted to control operation of the injection molding machine according to an injection cycle and a recovery profile, and a sensor coupled to the injection molding machine and the controller. The injection unit is adapted to receive and inject a molten plastic material into the mold cavity via the screw to form a molded part. The sensor is adapted to measure at least one variable during the recovery profile. Upon completion of the injection cycle, the controller commences the recovery profile where the screw is moved to the first position. Further, the controller adjusts an operational parameter of the injection molding machine based on the at least one measured variable.

In accordance with a third aspect, a non-transitory computer-readable storage medium stores processor-executable instructions. When executed, the instructions cause one or more processors to inject a molten polymer into the mold cavity according to the injection cycle using a screw that moves from a first position to a second position. Upon completion of the injection cycle, a recovery profile commences in which the screw is moved to the first position. Using a sensor, at least one variable is measured during the recovery profile. At least one operational parameter of the injection molding machine is measured based on the at least one measured variable during the recovery profile.

In accordance with a fourth aspect, a client device includes one or more processors, one or more interfaces, and transitory computer-readable storage medium stores processor-executable instructions. When executed, the instructions cause one or more processors to inject a molten polymer into the mold cavity according to the injection cycle using a screw that moves from a first position to a second position. Upon completion of the injection cycle, a recovery profile commences in which the screw is moved to the first position. Using a sensor, at least one variable is measured during the recovery profile. At least one operational parameter of the injection molding machine is measured based on the at least one measured variable during the recovery profile.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as the present invention, it is believed that the invention will be more fully understood from the following description taken in conjunction with the accompanying drawings. Some of the figures may have been simplified by the omission of selected elements for the purpose of more clearly showing other elements. Such omissions of elements in some figures are not necessarily indicative of the presence or absence of particular elements in any of the exemplary embodiments, except as may be explicitly delineated in the corresponding written description. None of the drawings are necessarily to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention.

Generally speaking, aspects of the present disclosure include systems and approaches for controlling an injection molding machine where operational parameters are adjusted to ensure a consistent molten material viscosity. In these systems and approaches, upon completion of the injection cycle (i.e., during a recovery portion), a recovery profile commences that is at least partially dependent on a desired operational pattern (i.e., in a closed loop manner) that is indicative of (and/or results in) high quality parts that remain within desired dimensional tolerances. Accordingly, the system can adjust operational parameters of the recovery process as needed in order for its output to match that of the operational pattern. As used herein, the phrase "commencing a pattern recognition portion of the recovery portion" means a controller commences the operations that cause the injection molding machine to operate in a manner that depends on the desired operational recovery profile or pattern.

In some examples, the operational pattern may be in the form of an operational recovery curve that can be identified during a validation phase. One such example of a suitable operational recovery curve is a back pressure curve, which in some forms may simply be a single set point. Because the back pressure exerted on the screw impacts viscosity of the molten plastic material, by measuring and adjusting the back pressure, the viscosity of the molten plastic material may be controlled. The back pressure curve may have a correlation to an ideal viscosity of the molten plastic material. As will be discussed in further detail below, the system may adjust operational parameters of the injection molding machine in order for its output to match that of the previously identified back pressure curve. By ensuring the machine's output during the recovery portion matches the back pressure curve, the described system will in turn ensure that the viscosity remains constant or near-constant; meaning in a subsequent injection cycle, the plastic material will begin with uniform or near-uniform viscosities, thereby limiting or reducing changes to the quality of the molded part.

Turning to the drawings, an injection molding process is herein described. The approaches described herein may be suitable for electric presses, servo-hydraulic presses, hydraulic presses, and other known machines. As illustrated in <FIG>, the injection molding machine <NUM> includes an injection unit <NUM> and a clamping system <NUM>. The injection unit <NUM> includes a hopper <NUM> adapted to accept material in the form of pellets <NUM> or any other suitable form. In many of these examples, the pellets <NUM> may be a polymer or polymer-based material. Other examples are possible.

The hopper <NUM> feeds the pellets <NUM> into a heated barrel <NUM> of the injection unit <NUM>. Upon being fed into the heated barrel <NUM>, the pellets <NUM> may be driven to the end of the heated barrel <NUM> by a reciprocating screw <NUM>. The heating of the heated barrel <NUM> and the compression of the pellets <NUM> by the reciprocating screw <NUM> causes the pellets <NUM> to melt, thereby forming a molten plastic material <NUM>. The molten plastic material <NUM> is typically processed at a temperature selected within a range of about <NUM> to about <NUM> (with manufacturers of particular polymers typically providing injection molders with recommended temperature ranges for given materials).

The reciprocating screw <NUM> advances forward from a first position 112a to a second position 112b and forces the molten plastic material <NUM> toward a nozzle <NUM> to form a shot of plastic material that will ultimately be injected into a mold cavity <NUM> of a mold <NUM> via one or more gates <NUM> which direct the flow of the molten plastic material <NUM> to the mold cavity <NUM>. In other words, the reciprocating screw <NUM> is driven to exert a force on the molten plastic material <NUM>. In other embodiments, the nozzle <NUM> may be separated from one or more gates <NUM> by a feed system (not illustrated). The mold cavity <NUM> is formed between the first and second mold sides <NUM>, <NUM> of the mold <NUM> and the first and second mold sides <NUM>, <NUM> are held together under pressure via a press or clamping unit <NUM>.

The press or clamping unit <NUM> applies a predetermined clamping force during the molding process which is greater than the force exerted by the injection pressure acting to separate the two mold halves <NUM>, <NUM>, thereby holding together the first and second mold sides <NUM>, <NUM> while the molten plastic material <NUM> is injected into the mold cavity <NUM>. To support these clamping forces, the clamping system <NUM> may include a mold frame and a mold base, in addition to any other number of components, such as a tie bar.

Once the shot of molten plastic material <NUM> is injected into the mold cavity <NUM>, the reciprocating screw <NUM> halts forward movement. The molten plastic material <NUM> takes the form of the mold cavity <NUM> and cools inside the mold <NUM> until the plastic material <NUM> solidifies. Upon solidifying, the press <NUM> releases the first and second mold sides <NUM>, <NUM>, which are then separated from one another. The finished part may then be ejected from the mold <NUM>. The mold <NUM> may include any number of mold cavities <NUM> to increase overall production rates. The shapes and/or designs of the cavities may be identical, similar to, and/or different from each other. For instance, a family mold may include cavities of related component parts intended to mate or otherwise operate with one another. In some forms, an "injection cycle" is defined as of the steps and functions performed between commencement of injection and ejection. Upon completion of the injection cycle, a recovery profile is commenced during which the reciprocating screw <NUM> returns to the first position 112a.

The injection molding machine <NUM> also includes a controller <NUM> communicatively coupled with the machine <NUM> via connection <NUM>. The connection <NUM> may be any type of wired and/or wireless communications protocol adapted to transmit and/or receive electronic signals. In these examples, the controller <NUM> is in signal communication with at least one sensor, such as, for example, sensor <NUM> located in or near the nozzle <NUM> and/or a sensor <NUM> located in or near the mold cavity <NUM>. In some examples, the sensor <NUM> is located at a leading end of the screw <NUM> and the sensor <NUM> is located in a manifold or a runner of the injection machine <NUM>. Alternatively, the sensor <NUM> may be located at any position ahead of the check ring of the screw <NUM>. It is understood that any number of additional real and/or virtual sensors capable of sensing any number of characteristics of the mold <NUM> and/or the machine <NUM> may be used and placed at desired locations of the machine <NUM>. As a further example, any type of sensor capable of detecting flow front progression in the mold cavity <NUM> may be used.

The controller <NUM> can be disposed in a number of positions with respect to the injection molding machine <NUM>. As examples, the controller <NUM> can be integral with the machine <NUM>, contained in an enclosure that is mounted on the machine, contained in a separate enclosure that is positioned adjacent or proximate to the machine, or can be positioned remote from the machine. In some embodiments, the controller <NUM> can partially or fully control functions of the machine via wired and/or wired signal communications as known and/or commonly used in the art.

The sensor <NUM> may be any type of sensor adapted to measure (either directly or indirectly) one or more characteristics of the molten plastic material <NUM> and/or portions of the machine <NUM>. The sensor <NUM> may measure any characteristics of the molten plastic material <NUM> that are known and used in the art, such as, for example, a back pressure, temperature, viscosity, flow rate, hardness, strain, optical characteristics such as translucency, color, light refraction, and/or light reflection, or any one or more of any number of additional characteristics which are indicative of these. The sensor <NUM> may or may not be in direct contact with the molten plastic material <NUM>. In some examples, the sensor <NUM> may be adapted to measure any number of characteristics of the injection molding machine <NUM> and not just those characteristics pertaining to the molten plastic material <NUM>. As an example, the sensor <NUM> may be a pressure transducer that measures a melt pressure (during the injection cycle) and/or a back pressure (during the recovery profile) of the molten plastic material <NUM> at the nozzle <NUM>.

As previously noted, the sensor <NUM> may measure a back pressure exerted on the screw <NUM>, but unlike in conventional systems where back pressure is measured on a trailing end of the screw <NUM>, in the present approaches, back pressure is measured on a leading end of the screw <NUM>. This positioning allows the sensor <NUM> to accurately measure the compressive pressure on the molten plastic material <NUM> as compared to measurements obtained at the trailing end of the screw <NUM> due to the compressible nature of the molten plastic material <NUM>, draw in the barrel, and other factors.

The sensor <NUM> generates a signal which is transmitted to an input of the controller <NUM>. If the sensor <NUM> is not located within the nozzle <NUM>, the controller <NUM> can be set, configured, and/or programmed with logic, commands, and/or executable program instructions to provide appropriate correction factors to estimate or calculate values for the measured characteristic in the nozzle <NUM>. For example, as previously noted, the sensor <NUM> may be programmed to measure a back pressure during a recovery profile. The controller <NUM> may receive these measurements and may translate the measurements to other characteristics of the molten plastic material <NUM>, such as a viscosity value.

Similarly, the sensor <NUM> may be any type of sensor adapted to measure (either directly or indirectly) one or more characteristics of the molten plastic material <NUM> to detect its presence and/or condition in the mold cavity <NUM>. In various embodiments, the sensor <NUM> may be located at or near an end-of-fill position in the mold cavity <NUM>. The sensor <NUM> may measure any number of characteristics of the molten plastic material <NUM> and/or the mold cavity <NUM> that are known in the art, such as pressure, temperature, viscosity, flow rate, hardness, strain, optical characteristics such as translucency, color, light refraction, and/or light reflection, and the like, or any one or more of any number of additional characteristics indicative of these. The sensor <NUM> may or may not be in direct contact with the molten plastic material <NUM>. As an example, the sensor <NUM> may be a pressure transducer that measures a cavity pressure of the molten plastic material <NUM> within the cavity <NUM>. The sensor <NUM> generates a signal which is transmitted to an input of the controller <NUM>. Any number of additional sensors may be used to sense and/or measure operating parameters.

The controller <NUM> is also in signal communication with a screw control <NUM>. In some embodiments, the controller <NUM> generates a signal which is transmitted from an output of the controller <NUM> to the screw control <NUM>. The controller <NUM> can control any number of characteristics of the machine, such as injection pressures (by controlling the screw control <NUM> to advance the screw <NUM> at a rate which maintains a desired value corresponding to the molten plastic material <NUM> in the nozzle <NUM>), barrel temperatures, clamp closing and/or opening speeds, cooling time, inject forward time, overall cycle time, pressure set points, ejection time, screw recovery speed, back pressure values exerted on the screw <NUM>, and screw velocity.

The signal or signals from the controller <NUM> may generally be used to control operation of the molding process such that variations in material viscosity, mold temperatures, melt temperatures, and other variations influencing filling rate are taken into account by the controller <NUM>. Alternatively or additionally, the controller <NUM> may make necessary adjustments in order to control for material characteristics such as viscosity. Adjustments may be made by the controller <NUM> in real time or in near-real time (that is, with a minimal delay between sensors <NUM>, <NUM> sensing values and changes being made to the process), or corrections can be made in subsequent cycles. Furthermore, several signals derived from any number of individual cycles may be used as a basis for making adjustments to the molding process. The controller <NUM> may be connected to the sensors <NUM>, <NUM>, the screw control <NUM>, and or any other components in the machine <NUM> via any type of signal communication approach known in the art.

The controller <NUM> includes software <NUM> adapted to control its operation, any number of hardware elements <NUM> (such as, for example, a non-transitory memory module and/or processors), any number of inputs <NUM>, any number of outputs <NUM>, and any number of connections <NUM>. The software <NUM> may be loaded directly onto a non-transitory memory module of the controller <NUM> in the form of a non-transitory computer readable medium, or may alternatively be located remotely from the controller <NUM> and be in communication with the controller <NUM> via any number of controlling approaches. The software <NUM> includes logic, commands, and/or executable program instructions which may contain logic and/or commands for controlling the injection molding machine <NUM> according to a mold cycle. The software <NUM> may or may not include an operating system, an operating environment, an application environment, and/or a user interface.

The hardware <NUM> uses the inputs <NUM> to receive signals, data, and information from the injection molding machine being controlled by the controller <NUM>. The hardware <NUM> uses the outputs <NUM> to send signals, data, and/or other information to the injection molding machine. The connection <NUM> represents a pathway through which signals, data, and information can be transmitted between the controller <NUM> and its injection molding machine <NUM>. In various embodiments this pathway may be a physical connection or a non-physical communication link that works analogous to a physical connection, direct or indirect, configured in any way described herein or known in the art. In various embodiments, the controller <NUM> can be configured in any additional or alternate way known in the art.

The connection <NUM> represents a pathway through which signals, data, and information can be transmitted between the controller <NUM> and the injection molding machine <NUM>. In various embodiments, these pathways may be physical connections or non-physical communication links that work analogously to either direct or indirect physical connections configured in any way described herein or known in the art. In various embodiments, the controller <NUM> can be configured in any additional or alternate way known in the art.

As illustrated in <FIG>, an example injection cycle <NUM> of a conventional injection molding machine <NUM> includes a number of distinct stages. While the illustrated example depicts a substantially constant pressure profile, other pressure profiles (e.g., a velocity controlled, high pressure injection molding process) may be used in conjunction with the approaches described herein.

During a first stage <NUM>, the molten plastic material <NUM> first fills the mold cavity <NUM>. In this stage <NUM>, the controller <NUM> increases the melt pressure to a substantially constant pressure value (e.g., approximately <NUM>,<NUM> psi) and then causes the melt pressure to hold at or close to this pressure value while the molten plastic material <NUM> fills the mold cavity <NUM>. The molten plastic material <NUM> then enters a pack/hold stage <NUM> where the melt pressure is maintained to ensure that all gaps in the mold cavity <NUM> are back filled. In these systems, the mold cavity <NUM> is filled from the end of the flow channel back towards the gate <NUM>. As a result, molten plastic material <NUM> in various stages of solidification is packed upon itself. In these approaches, the melt pressure is either raised or lowered based on the amount of cavity pressure measured. The degree of change is dependent on the amount of cavity pressure and a multiplier, as will be discussed below, which are determined during process validation and adjusted as needed.

During this process, upon the mold cavity <NUM> being substantially and/or completely filled with molten plastic material <NUM>, the sensed pressure within the mold cavity <NUM> will eventually become a non-zero value. The time it takes for the injection cycle to reach a non-zero cavity pressure can be defined as a "step time", which is equal to the time required to fill the mold cavity <NUM> (e.g., a "fill time") plus a process factor adjustment ("PFA") value. PFA is a multiplier to the amount of cavity pressure measured in the mold. As cavity pressure is measured, an adjustment to the melt pressure set point takes place based on a multiplier that is determined during the validation of the process (PFA). This multiplier can be adjusted as necessary to make a quality part. In the illustrated example of <FIG>, the overall step time corresponds to the duration of stage <NUM>, and therefore is intended to remain a fixed value. However, in some examples, the actual step time for each injection cycle may vary depending on material characteristics.

As illustrated by curve <NUM> in <FIG>, which depicts a sensed cavity pressure, during the injection cycle and upon the cavity being substantially completely filled, the cavity pressure rapidly increases to a maximum value, and subsequently decreases until it returns to a minimal value as the injection cycle is completed. In conventional injection systems, the cavity pressure curve <NUM> is merely an output of the injection system which may be used to provide data representative of the quality of the injection cycle. As previously noted, during a validation stage, a number of varying injection cycles are performed until a molded part having ideal and/or desirable characteristics is obtained. This ideal injection cycle will produce as an output a corresponding ideal pattern that is at least partially based on the fill time, fill pressure, and material characteristics. Accordingly, once it is determined that a suitable injection cycle has been performed that produces parts having suitable physical characteristics, the resulting cavity pressure curve, such as illustrated cavity pressure curve <NUM> may be used as a driving variable for the injection cycle. For example, <CIT> and <CIT> describe approaches for using a cavity pressure curve as an input for an injection cycle. In a similar manner, the suitable injection cycle may also produce an ideal recovery pattern which may be used during the recovery profile portion. This ideal recovery pattern may or may not include variable operational values.

As previously stated, during an injection molding cycle, the sensors <NUM>, <NUM> are adapted to measure at least one variable (such as, for example, a back pressure value) related to operation of the machine <NUM>. During operation and upon completion of the injection cycle, the controller <NUM> commences a recovery profile which may be stored in the software <NUM>. In some examples, the recovery profile may be commenced upon the controller <NUM> sending a signal to the machine that causes the mold cavity <NUM> to open and to eject the part from the mold <NUM>. The part may then complete necessary continued expansion and crosslinking to form a structurally sound molded part. For example, a structurally sound molded part may be free of divots, dwells, flash, partial fills, burns, tears, minimal imperfections such as sink marks and/or swirls on the surface layer, weakness at thickness changes, and may also have uniformity of mechanical properties.

As illustrated in <FIG>, upon completion of the injection cycle <NUM>, a recovery profile <NUM> commences where the screw <NUM> returns to the first position 112a. During the recovery profile <NUM>, an ideal recovery pattern in the form of an ideal back pressure set point <NUM> is identified and used as an input to control operation of the injection molding machine <NUM>. In other words, in this example, the back pressure set point <NUM> is used as the input which determines how the machine <NUM> should operate, while the sensor <NUM> provides feedback to the controller <NUM> to determine whether adjustments should be made to match the back pressure set point <NUM>. This back pressure set point <NUM> is used as a proxy for the viscosity of the molten plastic material <NUM>, meaning, by operating the machine <NUM> to obtain a desired back pressure value, the machine <NUM> will in turn obtain a desired molten plastic material <NUM> viscosity.

As illustrated in <FIG>, a back pressure curve <NUM> reflects the back pressure measured by the sensor <NUM>. Accordingly, the controller <NUM> may adjust the pressure exerted on the screw <NUM> in order to maintain the back pressure curve <NUM> to the back pressure profile <NUM>. Depending on the type of machine <NUM> being used, different valves and/or motors may be used to maintain and/or adjust the pressure exerted on the back of the screw <NUM>. For example, a servo motor may be used to turn the screw drive and control movement of the screw <NUM>, a flow control valve may be used, which controls the quantity of hydraulic fluid being exerted on the screw <NUM>, or a proportional valve may be used.

In operation, the controller <NUM> may cause the screw <NUM> to selectively increase and/or decrease the back pressure and thus shear the molten plastic material <NUM> more or less, respectively, thereby making the screw <NUM> expend different amounts of energy to return to the first position 112a. Accordingly, the screw <NUM> will impart additional heat into the molten plastic material <NUM>, thereby reducing its viscosity. The opposite operation may be performed in order to increase the viscosity of the molten plastic material <NUM>. As a result, the controller <NUM> will match the back pressure curve <NUM> to the back pressure profile <NUM>, and thus the corresponding viscosity of the molten plastic material <NUM> will remain constant and/or relatively constant. As illustrated by the screw velocity curve <NUM> in <FIG>, the controller <NUM> may adjust the screw velocity as a way to match the back pressure curve <NUM> with the back pressure profile <NUM>. Other examples of adjustments are possible, such as adjustments to the size and velocity of decompression, or temperature adjustments, in instances when a gradual change in viscosity occurs. Other instances may require a change in the back pressure setpoint or profile. Indicators of such instances may include variation in recovery time or changes in velocities, pressures, and times during the injection stage of the cycle.

Additionally or separately, the controller <NUM> may set an upper and/or a lower limit on acceptable measured back pressure values when compared to the back pressure profile <NUM>. In one example, the upper and lower limits of the measured values may be within approximately <NUM>% of the back pressure profile <NUM>. Other examples of suitable limits are possible.

Turning to <FIG> and <FIG>, it may be determined during the validation stage that applying a variable back pressure during the recovery profile <NUM>, <NUM> may result in a desired molten plastic material <NUM> viscosity. Accordingly, <FIG> illustrates a stepped back pressure profile <NUM>, and <FIG> illustrates a continuously variable back pressure profile <NUM>, each of which may selectively increase and/or decrease the back pressure. In each of these examples, the controller <NUM> will match the back pressure curve <NUM>, <NUM> to the back pressure profiles <NUM>, <NUM> by adjusting any one (or a combination) of the back pressure, screw velocity, and/or other measurements. Other examples of suitable back pressure profiles are possible.

In some approaches, other operational parameters or characteristics may be used to determine that changes should be made to the operational parameters of the machine <NUM> during the recovery profile <NUM>, <NUM>, <NUM>. For example, if, during recovery, it is determined that it is taking longer for the screw <NUM> to fully recover and return to the first position 112a, this may mean the viscosity of the molten plastic material <NUM> has increased. Accordingly, the controller <NUM> may increase the back pressure as previously described to reduce the viscosity. Further, it will be appreciated that the viscosity of the molten plastic material <NUM> is but one example of a characteristic that may be controlled for. In other examples, a desired melt density, decompression, and/or melt travel value may be proactively controlled for. Other examples are possible.

In some examples, the sensor <NUM> may be disposed remotely from the screw <NUM>, yet may still be in communication therewith. For example,<CIT>, describes the use of one or more external sensors as virtual sensors. Such a sensor or sensor arrangement may be used interchangeably with the sensor <NUM> described herein.

Further, in some examples, the controller <NUM> may incorporate machine learning techniques to automatically identify appropriate conditions for adjusting the back pressure to obtain a desired viscosity of the molten plastic material <NUM>. For example, the controller <NUM> may establish a scoring metric that determines when to adjust specific parameters of the machine <NUM> based on sensed input(s). Other examples are possible.

The above-described approaches may be used in conjunction with any injection process where the previously-identified pattern is used to drive at least a portion of the recovery profile. These approaches may be used in the formation of any number of different molded parts constructed from a variety of materials such as, for example silicone and metal parts.

Claim 1:
A method for controlling an injection molding machine having a mold forming a mold cavity, the injection molding machine being controlled according to an injection cycle, the method comprising:
injecting a molten polymer into the mold cavity according to the injection cycle using a screw that moves from a first position to a second position;
upon completion of the injection cycle, commencing a recovery profile in which the screw is moved to the first position;
measuring, using a sensor, at least one variable during the recovery profile; and
adjusting at least one operational parameter of the injection molding machine based on the at least one measured variable during the recovery profile
characterized in that the at least one variable comprises a nozzle pressure, and the operational parameter comprises a back pressure, the back pressure being adjusted according to the sensed nozzle pressure.