Stabilized adaptive hydraulic system pressure in an injection molding system

In one aspect, there is provided an injection molding system configured to operate in a plurality of cycles. The system comprises, amongst other things, a controller that is configured for performing a comparison of a variable pressure setpoint with a target pressure value. The controller is configured to, when the target pressure value is less than the variable pressure setpoint by at least a predetermined lower bound, (i) decrease the variable pressure setpoint to a reduced variable pressure setpoint and (ii) not further decrease the variable pressure setpoint from the reduced variable pressure setpoint until the pump assembly operates for a plurality of stabilizing cycles at the reduced variable pressure setpoint.

BACKGROUND

In hydraulic systems, including, for example, an injection molding system, it is desirable to minimize the consumption of energy. The energy consumed in a hydraulic system is a function of various characteristics of the system, such that altering one or more of these characteristics will alter the energy consumed.

Specifically, it is well known that the power required by a hydraulic system can be defined as the hydraulic fluid pressure times its volumetric flow rate. The volumetric flow rate, in turn, can be defined as the hydraulic fluid flow cross-sectional area times the flow velocity.

In an injection molding system, the flow rate inputs of flow cross-sectional area and flow velocity (in other words, size and speed) correspond to those properties of the actuator. Thus, an injection molding system's hydraulic power can be defined as the system pressure times the actuator cross-sectional area times the actuator speed. In order to reduce the consumption of energy, one or more of these three parameters—system pressure, actuator area, and actuator speed—must be reduced.

Because an injection molding system has fixed actuator sizes, it is not feasible to reduce their size during operation of the injection molding system. And while the actuator speed can be reduced, this is not desirable because actuator speed and system output are directly correlated, so reducing speed would reduce output.

Thus, to reduce energy consumption while maintaining output, the most feasible option is to reduce system pressure.FIG.1is a graph that illustrates the relationship between system pressure, energy, and output in injection molding systems generally. As system pressure is reduced in an injection molding system, the specific energy consumed at a given quantity of output is also reduced.

A hydraulic system may be designed to operate over a number of process cycles, and various functions may take place during each cycle. In an injection molding system, these functions may relate to, at a high level, clamping of the mold, injection of plastic material, cooling of the injected plastic, and ejection of the molded part. More specifically, such functions may include, for example, and among others, mold closing, clamp-up, injection fill, injection hold, unclamp, mold opening, ejector-forward, ejector-back, transfer, packing, and carriage. These functions have different pressure requirements, so within an injection molding system cycle, the pressure necessary to perform these functions may have largely fluctuating values. For a given function, the required pressure may also vary at different components of the injection molding system—for example, the pressures at the pump(s), accumulator(s), clamp supply, and injection supply may have different values. In order for the injection molding system to operate, its system pressure must have a value at least as great as the greatest required value of component pressure in a cycle. However, to the extent the system pressure is greater than the greatest required value of component pressure, this surplus represents excess energy that was unnecessarily consumed.FIGS.2A and2Bare graphs that illustrate this surplus in system pressure for injection supply in an injection molding system. The system pressure is reduced in this example from 220 bar inFIG.2Ato 190 bar inFIG.2B, reducing the surplus system pressure over the peak component pressure, and thereby reducing the energy consumed by the system.

Examples of known injection molding systems and components thereof are disclosed in WO 2010/144993 and US 2015/0037448 A1, including via additional references disclosed therein.

SUMMARY OF THE INVENTION

In one aspect of the present invention, there is provided an injection molding system configured to operate in a plurality of cycles. The system comprises a pump assembly, a proportional pump control valve operatively connected to the pump assembly, a sensor and a controller. The proportional pump control valve is configured to provide a variable pressure setpoint of the injection molding system equal to a magnitude of pressure of hydraulic fluid within the proportional pump control valve. The sensor is configured to detect the magnitude of pressure hydraulic fluid within the proportional pump control valve and to send a signal to the controller representative of the variable pressure setpoint. The controller is configured to control a flowrate of hydraulic fluid flowing out of the proportional pump control valve. The variable pressure setpoint is configured to change based on the flowrate of hydraulic fluid flowing out of the proportional pump control valve. The controller is configured to perform a comparison of the variable pressure setpoint with a target pressure value. Upon performing the comparison of the variable pressure setpoint with the target pressure value, the controller is configured to, when the target pressure value is less than the variable pressure setpoint by at least a predetermined lower bound, (i) decrease the variable pressure setpoint to a reduced variable pressure setpoint and (ii) not further decrease the variable pressure setpoint from the reduced variable pressure setpoint until the pump assembly operates for a plurality of stabilizing cycles at the reduced variable pressure setpoint.

Other aspects and features of the present invention are identified in the claims.

Other aspects and features of the non-limiting embodiments may now become apparent to those skilled in the art upon review of the following detailed description of the non-limiting embodiments with the accompanying drawings.

The drawings are not necessarily to scale and may be illustrated by phantom lines, diagrammatic representations and fragmentary views. In certain instances, details not necessary for an understanding of the embodiments (and/or details that render other details difficult to perceive) may have been omitted.

DETAILED DESCRIPTION OF THE NON-LIMITING EMBODIMENTS

The present invention is related to a hydraulic system. In specific embodiments of the invention described below, the hydraulic system is used as part of an injection molding system. However, those skilled in the art will recognize that the hydraulic system could be used in systems other than an injection molding system.

Referring now toFIG.3, an example of an injection molding system900is shown. The molding system900is configured to support and to use a hydraulic circuit of the present invention, including the examples ofFIGS.4and5. Other aspects and components of the injection molding system900may be known and may include those disclosed in WO 2010/144993 and US 2015/0037448 A1, including the references disclosed therein. For example, aspects of the injection molding system900depicted inFIG.3are described in US 2015/0037448 A1. According to the example ofFIG.3, the injection molding system900includes (and is not limited to) an extruder assembly, a clamp assembly, a runner system, and/or a mold assembly918. By way of example, the extruder assembly902is configured to prepare, in use, a heated, flowable resin, and is also configured to inject or to move the resin from the extruder assembly902toward the runner system916. Other names for the extruder assembly902may include “injection unit,” “melt-preparation assembly,” etc. By way of example, the clamp assembly904includes (and is not limited to): a stationary platen906, a movable platen908, a rod assembly910, a clamping assembly912, and/or a lock assembly914. The stationary platen906does not move; that is, the stationary platen906may be fixedly positioned relative to the ground or floor. The movable platen908is configured to be movable relative to the stationary platen906. A platen-moving mechanism (not depicted but known) is connected to the movable platen908, and the platen-moving mechanism is configured to move, in use, the movable platen908. The rod assembly910extends between the movable platen908and the stationary platen906. The rod assembly910may have, by way of example, four rod structures positioned at the corners of the respective stationary platen906and the movable platen908. The rod assembly910is configured to link the movable platen908to the stationary platen906. A clamping assembly912is connected to the rod assembly910. The stationary platen906is configured to support (or configured to position) the position of the clamping assembly912. The lock assembly914is connected to the rod assembly910, or may alternatively be connected to the movable platen908. The lock assembly914is configured to selectively lock and unlock the rod assembly910relative to the movable platen908. By way of example, the runner system916is attached to, or is supported by, the stationary platen906. The runner system916is configured to receive the resin from the extruder assembly902. By way of example, the mold assembly918includes (and is not limited to): a mold-cavity assembly920and a mold-core assembly922that is movable relative to the mold-cavity assembly920. The mold-core assembly922is attached to or supported by the movable platen908. The mold-cavity assembly920is attached to or supported by the runner system916, so that the mold-core assembly922faces the mold-cavity assembly920. The runner system916is configured to distribute the resin from the extruder assembly902to the mold assembly918.

In operation, the movable platen908is moved toward the stationary platen906so that the mold-cavity assembly920is closed against the mold-core assembly922, so that the mold assembly918may define a mold cavity configured to receive the resin from the runner system916. The lock assembly914is engaged so as to lock the position of the movable platen908so that the movable platen908no longer moves relative to the stationary platen906. The clamping assembly912is then engaged to apply a clamping pressure, in use, to the rod assembly910, so that the clamping pressure then may be transferred to the mold assembly918. The extruder assembly902pushes or injects, in use, the resin to the runner system916, which then the runner system916distributes the resin to the mold cavity structure defined by the mold assembly918. Once the resin in the mold assembly918is solidified, the clamping assembly912is deactivated so as to remove the clamping force from the mold assembly918, and then the lock assembly914is deactivated to permit movement of the movable platen908away from the stationary platen906, and then a molded article may be removed from the mold assembly918.

It will be appreciated that the injection molding system900may include more than two platens. According to an example, the injection molding system900includes (and is not limited to) a third platen (not depicted), which is also called a “clamping platen” that is known in the art and thus is not described here in greater detail.

Referring now toFIG.4, a schematic for a hydraulic circuit is shown at100. The hydraulic circuit100is configured to actuate one or more functions of the injection molding system900, for example, mold closing, clamp-up, injection fill. According to the example ofFIG.4, the hydraulic circuit100includes a pump assembly110, a motor assembly112, a pump actuator assembly116, a hydraulic fluid filter115, an accumulator check valve117, one or more accumulator assemblies118, a pump compensator valve assembly120, a proportional pump control valve150, a reservoir160, and a controller170.

The pump assembly110is configured to pump hydraulic fluid from the reservoir160to other components of the hydraulic circuit100. In the presently illustrated embodiment, the pump assembly110is a variable displacement piston pump, although it is not particularly limited and can include both fixed and variable displacement pumps, as is known to those skilled in the art. The pump assembly110is operatively connected to motor assembly112, to the reservoir160, and to one or more accumulator assemblies118. The pump assembly110is also operatively connected to, and configured to be controlled by a valve. For example,150Control Valve is configured to control the pump assembly110by changing its displacement. Alternatively if so equipped the pump can be controlled with a variable speed motor, the RPM can be controlled, or both RPM and displacement can be controlled.

The motor assembly112is configured to actuate movement of the pump assembly110. In the presently illustrated embodiment, the motor assembly112is a fixed-RPM motor, although it is not particularly limited and can include variable RPM motors or servo motors. The motor assembly112is operatively connected to, and configured to be controlled by, the drive. For example, the servo drive or variable frequency drive is configured to control the motor assembly120by changing its rpm, or torque limits.

The one or more accumulator assemblies118are configured to store hydraulic fluid under pressure generated by the pump assembly110. The one or more accumulator assemblies118are operatively connected to the pump assembly110via the accumulator check valve117and the hydraulic fluid filter115. The accumulator check valve117is configured to prevent the one or more accumulator assemblies118from discharging through the hydraulic fluid filter115and the pump assembly110while the motor assembly112is not in operation. The hydraulic fluid filter115is configured to filter the hydraulic fluid flowing to one or more accumulator assemblies118.

The pump compensator valve assembly120is configured to control the flow of hydraulic fluid to the actuator assembly116and to the proportional pump control valve150while the hydraulic fluid pressure has a value that is outside of preset setpoints. The pump compensator valve assembly120is operatively connected to the pump assembly110, to the actuator assembly116, and to the proportional pump control valve150. The pump compensator valve assembly120includes a maximum pump compensator valve130and a minimum pump compensator valve140. The maximum pump compensator valve130is configured to provide a preset maximum pressure setpoint of the injection molding system900, and the minimum pump compensator valve140is configured to provide a preset minimum pressure setpoint of the injection molding system900. In an example embodiment, the preset maximum pressure setpoint is 230 bar and the preset minimum pressure setpoint is 20 bar. In an example embodiment, each of the maximum pump compensator valve130and the minimum pump compensator valve140includes a set screw that is configured to be adjusted prior to operation of the injection molding system900; adjustment of the set screw changes the value of the spring force applied by the corresponding pump compensator valve and thus its preset pressure setpoint. The pump assembly110is configured to destroke when the hydraulic fluid pressure reaches the preset maximum pressure setpoint, such that this pressure value is maintained. In particular, when the system pressure (i) is below the minimum the valve140directs flow to the reservoir160through control valve150, causing the pump to go to maximum displacement, (ii) crosses the minimum threshold, (iii) crosses the maximum threshold, and (iv) is above the maximum the valve130blocks flow to the reservoir160and through control valve150, causing the pump to go to minimum displacement.

The actuator assembly116is configured to impart a force to the pumps internal swashplate. The force is used, for example, to change the displacement of the pump assembly110.

The proportional pump control valve150is configured to provide a variable pressure setpoint of the injection molding system900, within the end limits of valves130and140, and thereby control the system pressure of the injection molding system900. The proportional pump control valve150is operatively connected to the reservoir160. In the presently illustrated embodiment, the proportional pump control valve150is operatively connected to the reservoir160via a supply line154. The proportional pump control valve150is operatively connected to a sensor180. The sensor180is configured to detect pressure within the proportional pump control valve150and to send a signal representative of the pressure detected by the sensor180to the controller170. In the presently illustrated embodiment, the sensor180is a transducer. The proportional pump control valve150is operatively connected to, and configured to be controlled by, the controller170. For example, the controller170is configured to send a voltage signal to the proportional pump control valve150. The proportional pump control valve150is configured to, upon receipt of the voltage signal, permit flow of hydraulic fluid to the reservoir160, and thereby provide a variable pressure setpoint that is lower than the preset maximum pressure setpoint. In an example embodiment, the proportional pump control valve150is a variable displacement valve, whereby the voltage signal sent by the controller170governs the position of a spool within the proportional pump control valve150, thereby causing the orifice of the proportional pump control valve150to change in size depending on the voltage signal, such that hydraulic fluid flows at changing flowrates—or not at all—along the supply line154to the reservoir160. In this manner, changes in the size of the orifice of the proportional pump control valve150change pressure of the hydraulic fluid flowing through the proportional pump control valve150, thus changing the variable pressure setpoint and ultimately changing the system pressure. The reservoir160is configured to be a source of and receptacle for hydraulic fluid.

The hydraulic circuit100is thus configured to perform the following operation. When the motor assembly112operates to actuate movement of the pump assembly110, the pump assembly110pumps hydraulic fluid from the reservoir160to the pump compensator valve assembly120and in turn to the actuator assembly116and the proportional pump control valve150. The pump assembly110also pumps hydraulic fluid to the one or more accumulator assemblies118. With the presence of the voltage signal from the controller170to the proportional pump control valve150, the hydraulic fluid is restricted or not permitted to flow from the proportional pump control valve150to the reservoir160, and thus flows to the actuator assembly116. If there is no voltage signal the valve150will not restrict the oil flow and the “orifice” will be at maximum size. The pressure in the pump control circuit will decrease. If the minimum pressure setting of control valve140is reached, control valve140will close or restrict the oil flow into hose142diverting flow to actuator116in attempt to increase the displacement and increase the pump pressure above the minimum setpoint. As the pump assembly110continues to pump hydraulic fluid within the hydraulic circuit100, the pressure of the hydraulic fluid—corresponding to the system pressure of the injection molding system900—will continue to increase. In the event of a failure of the proportional pump control valve150or the controller170, the maximum pressure compensator valve130governs, and the system pressure will rise until it equals the preset maximum pressure setpoint. In normal operation, the proportional pump control valve150governs, and the system pressure will rise until it equals the variable pressure setpoint, as determined based on the voltage signal sent by the controller170. Depending on one or more system parameters, the voltage signal will change during operation, resulting in corresponding changes to the variable pressure setpoint and hence achieving adaptive system pressure.

Referring now toFIG.5, a schematic for a hydraulic circuit according to another embodiment is shown at200. The hydraulic circuit200is configured to actuate one or more functions of the injection molding system900. According to the example ofFIG.5, the hydraulic circuit200includes a first pump assembly110, a first actuator assembly116, a first pump compensator valve assembly120, a second pump assembly210, a second actuator assembly216, a second pump compensator valve assembly220, a motor assembly112, a hydraulic fluid filter115, an accumulator check valve117, one or more accumulator assemblies118, a proportional pump control valve150, a reservoir160, and a controller170.

It will be appreciated that, in accordance with the teachings herein, the injection molding system900may also be adapted to utilize three pump assemblies working with the proportional pump control valve150. In accordance with the teachings herein, the injection molding system900may also be adapted to utilize an even greater number of pump assemblies by increasing the size/output/capacity of the proportional pump control valve150or quantity of proportional pump control valves, to ensure enough hydraulic fluid can flow to the reservoir160.

Referring now toFIG.6, a flowchart of an example process of the controller170on the molding system900is shown at1000.

At step1010, the controller170checks whether the injection molding system900is in production cycles. Production cycles are in contrast to other cycle modes such as dry cycle when the injection unit is not engaged and no parts are made even though mold are being closed and opened in each cycle. Dry cycle is sometimes called empty cycle. Production cycles are sometimes called normal cycles. For example, the injection molding system900may be deemed not in production cycles if it is in any of the following modes: idle, calibration, mold set, manual, dry cycle, factory test, semi, ejector boosters active, and mold vent cleaning cycles. If yes, the process1000moves to step1020. If no, the process1000moves to step1025.

At step1020, the controller170checks whether a predetermined number of baseline cycles have been completed. The first cycle after auto start is counted as 1, any subsequent cycle will increase the count by one. “Auto Start” means the start of production cycle mode. If the predefined number is 10, the predefined number of cycles are completed when the count reaches 10. As further discussed below, the baseline cycles may be performed both in connection with startup of the process1000and in further iterations of the process1000when restarting pressure adaptation. If yes, the process1000moves to step1030. If no, the process1000moves to step1025.

At step1025, the pump assembly110operates for the predetermined number of baseline cycles at a predetermined standard pressure value. The so predetermined standard pressure is set by the controller170and needs to be in the range between the minimum limit set by valve140and maximum limit set by valve130. In separate example embodiments, the predetermined number of baseline cycles is 10 cycles and 20 cycles, although a different predetermined number of baseline cycles may be selected in accordance with the present invention. The process1000then moves to step1026.

At step1026, the controller170determines and logs the baseline performance of the injection molding system900. The baseline performance refers to one or more functions of the injection molding system900, and can include the time durations of the following functions, among others: mold closing, mold opening, clamp-up, unclamp, and/or ejector-forward. The baseline performance is determined based on measurements from one or more sensors associated with the functions, such as transducers. Baseline performance in the current implementation is regarding motion time specifically, although it can expand to any other criteria. The process1000then moves to step1120.

At step1030, the controller170determines and sets a target pressure value. The target pressure value is less than the predetermined standard pressure value but not small enough to result in a deviation from the baseline performance determined at step1026. In an example embodiment, the controller170sets the target pressure value to the highest value among the lower limits of pressure value imposed by one or more functions of the injection molding system900. These functions may include, for example, the functions measured during step1026. In an example embodiment, the lower limits of pressure value are determined using measurement and mathematical modeling. That is, for any given function, the lower limit of pressure value for that function can be determined based on measurement of its mechanical characteristics, mathematical modeling of its mechanical characteristics, or both, where the lower limit is the greater of the pressure value determined from the measurements or model. The mechanical characteristics of a function that can be measured include force, pressure, acceleration, and velocity, and physical characteristics associated with the function, including mass and area, can be used with the function's mechanical characteristics to determine its lower limit of pressure. Mathematical models can be used, for example, for functions that are sufficiently fast or dynamic so as to limit the accuracy of measurements, for the purpose of estimate the minimum pressure required to deliver performance of those functions. The process1000then moves to step1040.

At step1040, the controller170checks whether the pressure of the one or more accumulator assemblies118is lower than a predetermined accumulator pressure limit. In separate example embodiments, the predetermined accumulator pressure limit is 170 bar and 174 bar, although a different predetermined accumulator pressure limit may be selected in accordance with the present invention. If yes, the process1000moves to step1045. If no, the process1000moves to step1050.

At step1045, the controller170increases the variable pressure setpoint by an amount equal to the difference between the pressure of the one or more accumulator assemblies118and the predetermined accumulator pressure limit. The process1000then moves to step1050.

At step1050, the controller170checks whether the cycle/function time duration is longer than the corresponding baseline time duration determined at step1026. If yes, the process1000moves to step1055. If no, the process1000moves to step1060.

At step1055, the controller170increases the target pressure value to the value of the setpoint before the most recent drop in step1075. The process then moves to step1060.

At step1060, the controller170checks whether the target pressure value is greater than the variable pressure setpoint of the injection molding system900. If yes, the process1000moves to step1065. If no, the process moves to step1070.

At step1065, the controller170increases the variable pressure setpoint to the target pressure value. In an example embodiment, the controller170does so by causing the proportional pump control valve150to decrease the flowrate of hydraulic fluid to the reservoir160. The process then moves to step1080.

At step1070, the controller170checks whether a predetermined number of stabilizing cycles have been completed since the most recent decrease in the variable pressure setpoint. For the purposes of step1070, in the cycle immediately after the predetermined number of baseline cycles have been completed, the predetermined number of stabilizing cycles are deemed to have been completed since the most recent decrease in target pressure. Since the number of base line cycles is chosen to be larger than the number of stabilizing cycles, there is no need to repeat the number of stabilizing cycles immediately after the baseline cycles. In an example embodiment, the predetermined number of stabilizing cycles is 5 cycles, although a different predetermined number of stabilizing cycles may be selected in accordance with the present invention. If yes, the process1000moves to step1075. If no, the process1000moves to step1080.

At step1075, the controller170decreases the variable pressure setpoint to a value approaching the target pressure value. In an example embodiment, the controller170does so by causing the proportional pump control valve150to increase the flowrate of hydraulic fluid to the reservoir160. In an example embodiment, the decrease in the variable pressure setpoint is equal, or approximately equal, to a predetermined percentage of the difference between the variable pressure setpoint and the target pressure value. In an example embodiment, the decrease in the variable pressure setpoint is also limited such that it is within, or approximately within, a predetermined bound of pressure values. For example, the predetermined percentage may be 61.8%, and the predetermined bound may be 1 bar to 10 bar, inclusive, although a different predetermined percentage and/or predetermined bound of pressure values may be selected in accordance with the present invention. In this example, if the decrease in the variable pressure setpoint would be greater than the upper bound, it is limited to the upper bound, while if the decrease in the variable pressure setpoint would be less than the lower bound, it does not take place, and instead there is no change in the variable pressure setpoint. The process1000then moves to step1080.

At step1080, the controller170sets an updated value of the variable pressure setpoint, when applicable. The process1000then moves to step1090.

At step1090, the controller170checks whether relevant setpoints have been changed. As non-limiting examples, the relevant setpoints may be changeable by an operator of the injection molding system900and include but not limited the following setpoints: mold open position, mold closing speed, clamp tonnage, injection fill rate, etc. If yes, the process1000then moves to step1095. If no, the process1000then moves to step1100.

At step1095, the controller170causes the injection molding system900to restart pressure adaptation and reestablish baseline performance. For example, it does so by treating the predetermined number of baseline cycles not to have been completed. The process1000then moves to step1020.

At step1100, the controller170checks whether the hold/cooling time has decreased. If yes, the process1000moves to step1105. If no, the process1000moves to step1110. Hold time and cooling time are user setpoints on HMI and the controller keeps tracking if they are changed by the user. The controller records the event, amount, and the direction (increase or decrease) of the change.

At step1105, the controller170increases the variable pressure setpoint to compensate for the decrease in accumulator pressure charging time duration. Accumulator pressure charging typically occurs during the injection-hold and injection-cooling functions, in which oil consumption is at a minimum. If the accumulator charging time duration decreases, then the pressure of the one or more accumulator assemblies118will decrease and may be unable to support remaining functions of the current cycle, such as unclamp and mold-opening. In an example embodiment, the compensation for the decrease in accumulator charging time duration is performed using the accumulator pressure charging rate that is calibrated in a state of minimum oil consumption. For example, the state of minimum oil consumption can include the clamp-up and injection hold functions and exclude the transfer and packing functions. In an example embodiment, the controller170increases the variable pressure setpoint by causing the proportional pump control valve150to decrease the flowrate of hydraulic fluid to the reservoir160. The process1000then moves to step1110.

At step1110, the pump assembly110operates at the reduced pressure. The process1000then moves to step1120. At step1110, the pump assembly110operates for all cycles except for those cycles or modes that are subject to conditions in1025.

At step1120, the process1000continues and moves to step1010.

As exemplified by example process1000, the injection molding system900can operate to adapt the system pressure of the injection molding system900based on one or more inputs of the system.

Referring now toFIG.7, a graph of variable pressure setpoint over cycles in an example operation of the injection molding system900is shown at600. In the graph600, the y-axis is the variable pressure setpoint, measured in bar, and the x-axis is the number of completed cycles.

Prior to cycle 1, the variable pressure setpoint is approximately 220.0 bar. In an example embodiment performing the process1000, this represents the predetermined standard pressure value. At the predetermined standard pressure value, the variable pressure setpoint is lower than the preset maximum pressure setpoint, which is 230 bar in the example.

From cycle 1 to cycle 10, the pump assembly110operates for 10 cycles at a variable pressure setpoint of approximately 220.0 bar. In an example embodiment performing the process1000, this represents the process1000iterating through step1025for the predetermined number of baseline cycles—here, 10 cycles.

During cycle 11, the variable pressure setpoint is decreased to approximately 210.0 bar. In an example embodiment performing the process1000, this represents the process1000now proceeding through step1030and step1075within a single iteration. More specifically, at step1030, the target pressure value is set to a value that is less than the predetermined standard pressure value. At step1070, the controller170determines that the predetermined number of baseline cycles was completed with cycle 10, so at step1075, it decreases the variable pressure setpoint to a value—here, approximately 210.0 bar—approaching the target pressure value. From cycle 11 to cycle 15, the pump assembly110operates for 5 cycles at the variable pressure setpoint of approximately 210.0 bar. In an example embodiment performing the process1000, this represents the process1000proceeding from step1075as discussed above through step1110, then iterating for 4 more cycles proceeding directly through step1070and step1080and not step1075, for a total that is the predetermined number of stabilizing cycles—here, 5 cycles. During cycle 16, the variable pressure setpoint is decreased to approximately 200.0 bar. In an example embodiment performing the process1000, this represents the process1000again proceeding through step1030and step1075within a single iteration. At step1070, the controller170determines that the predetermined number of stabilizing cycles was completed with cycle 15, so at step1075, it decreases the variable pressure setpoint to a value—here, approximately 200.0 bar—approaching the target pressure value.

From cycle 16 to cycle 20, the pump assembly110operates for 5 cycles at the variable pressure setpoint of approximately 200.0 bar. In an example embodiment performing the process1000, this represents the process1000again proceeding from step1075as discussed above through step1110, then iterating for 4 more cycles proceeding directly through step1070and step1080and not step1075, for a total that is the predetermined number of stabilizing cycles.

During cycle 21, the variable pressure setpoint is decreased to approximately 193.8 bar. In an example embodiment performing the process1000, this represents the process1000again proceeding through step1030and step1075within a single iteration. At step1070, the controller170determines that the predetermined number of stabilizing cycles was completed with cycle 20, so at step1075, it decreases the variable pressure setpoint to a value—here, approximately 193.8 bar—approaching the target pressure value.

During cycle 22, the variable pressure setpoint is increased to approximately 200.0 bar, representing an increase equal to the decrease that took place during cycle 21. In an example embodiment performing the process1000, this represents the process1000proceeding through either or both of step1045and step1055, and then through step1065, within a single iteration. As a more specific example, this represents the process1000proceeding through step1050, at which the controller170determines that the most recently measured ejector-forward time duration is greater than the ejector-forward time duration that was determined during baseline performance. Accordingly, the process1000proceeds directly through step1055and increases the target pressure value by an amount equal to the previous decrease. Within the same iteration, the process1000then proceeds through step1060, where the controller170determines that the target pressure value is greater than the variable pressure setpoint, and then directly through step1065, where the controller170increases the variable pressure setpoint to the target pressure value—here, approximately 200.0 bar. The target pressure is 190 bar in cycle 20, remains at 190 bar in cycle 21. At the end of cycle 21 and before starting cycle 22, the control detected an increase of cycle time or function step time, it rolled the pressure back to 200 bar by undoing the previous pressure drop. At the same time, the control also changes the target pressure to be the same as the pressure setpoint, 200 bar in this case. From cycle 22 to 26, since the cycle time is not affected due to higher pressure (200 bar) than the pressure used in cycle 21 (193.8 bar), the algorithm doesn't go through step1055. The target pressure that is determined in step1030by the model remains at 190 bar (not revised higher). Due to another criteria that kicks in when step1055is triggered by the condition in1050, the pressure drop described in step1075is limited by a small value of 1 bar. Note that in cycle 37, the cycle time is impacted again and the algorithm trigged step1055the second time. It is in this instance that the target pressure settles at 198 bar. From cycle 22 to cycle 42, the injection molding system900operates with similar behavior to that of cycle 10 to cycle 22 discussed above. In an example embodiment performing the process1000, this represents the process1000proceeding through iterations of stabilizing cycles, one-cycle decreases in variable pressure setpoint, and a one-cycle increase in variable pressure setpoint offsetting the previous decrease.

During cycle 42, the variable pressure setpoint has essentially converged to the target pressure value. In an example embodiment performing the process1000, this represents the process1000proceeding through step1075, where the variable pressure setpoint is either equal or close enough to the target pressure value or that it does not decrease at step1075. In an example embodiment where the minimum decrease in target pressure value must be approximately 1 bar, the variable pressure setpoint can be within 1 bar above the target pressure value.

After cycle 42, the pump assembly110operates for an indefinite number of cycles at the stabilized variable pressure setpoint—here, approximately 198.0 bar. In an example embodiment performing the process1000, this will continue until an event causes a change in target pressure. The graph600thus demonstrates how, in one aspect of the present invention, decreases in the variable pressure setpoint gradually stabilize to an optimal value.

It is to be understood that the present invention is not limited to the disclosed example embodiments described above. The present invention is intended to cover various modifications and equivalent arrangements, such as are included within the scope of the claims. It may be appreciated that the embodiments, systems, components, and other items described above may be connected with each other as may be required to perform desired functions and tasks that are with the scope of persons of ordinary skill in the art to make such combinations and permutations without having to describe each and every one of them in explicit terms.