Metering device
The dosing device with sensors and control elements addresses energy waste by precisely supplying granules to the injection molding machine, enhancing measurement accuracy and reducing overheating.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ALPLA WERKE ALWIN LEHNER
- Filing Date
- 2025-11-28
- Publication Date
- 2026-06-04
AI Technical Summary
Energy waste occurs due to cooled plastic granules in the pipe connecting the dryer to the metering mixer, as they need to be reheated in the injection molding machine, and existing systems lack precision in supplying the required amount of granules.
A dosing device with controllable closure elements, sensors, and a control system that adjusts granule supply based on fill levels to match the demand of the injection molding machine, minimizing excess supply and heat loss.
The solution ensures precise granule supply, reducing energy waste by preventing overheating and improving measurement accuracy, making it adaptable to existing systems.
Smart Images
Figure EP2025084689_04062026_PF_FP_ABST
Abstract
Description
[0001] 1040-27087 1 28.11.2025
[0002] Dosing device
[0003] Field of invention
[0004] The invention relates to a metering device for metering plastic granules from a dryer according to the preamble of claim 1, a feeding device for feeding an injection molding machine according to claim 8 and a method for metering plastic granules from a dryer into a metering mixer according to claim 9.
[0005] State of the art
[0006] An injection molding machine is fed with plastic granules or powder via a metering mixer. Before being fed into the injection molding machine, the granules must be dried in a dryer, especially if the plastic is hygroscopic. The granules are typically dried in the dryer at a temperature of approximately 180 °C.
[0007] The dryer is connected to the metering mixer via a pipe that can have a diameter of up to 110 mm and a length of up to 4000 mm. The pipe is pre-filled with granules, which are drawn from the metering mixer as needed and conveyed to the injection molding machine.
[0008] The dried granules are stored in the tube and cool down accordingly before they need to be reheated in the injection molding machine to melt the plastic granules. Cooling the granules in the tube represents a waste of energy.
[0009] Object of the invention
[0010] The disadvantage of the described state of the art results in the task of creating a device and a method that will prevent the described energy waste.
[0011] Description
[0012] The problem is solved in a dosing device for dosing plastic granules from a dryer into a dosing mixer of an injection molding machine by the means specified in the characterizing section of claim 1 1040-27087 2 28.11.2025
[0013] Features. Further developments and / or advantageous embodiments are the subject of the dependent patent claims.
[0014] The invention is characterized in that the dosing device comprises a controllable closure element, in particular a slide gate, which can close and open the dryer outlet into the pipe, a plurality of sensors which can detect different granule fill levels in the dosing mixer and generate corresponding sensor signals, and a control device which can open and close the closure element depending on the sensor signals. These elements enable the dosing device to supply precisely the amount of granules required by the injection molding machine for one injection molding cycle to the dosing mixer. This reliably prevents heat losses due to excess granules being supplied, which would have been heated in the dryer. The granules are supplied as needed by a demand-controlled system that regulates the closure element.The dosing device is extremely flexible and can be quickly retrofitted to existing feeding devices or be a component of a new feeding device.
[0015] It has proven advantageous to position the first, second, and third sensors at heights on the dosing mixer such that they can detect low, high, and full fill levels. This allows for the selection of appropriate fill level heights. The optimal sensor positioning depends on a variety of parameters, such as the required batch size for an injection molding cycle, the cross-section of the dosing mixer, and the machine's cycle time. Retrofitting the sensors to an existing system is also possible.
[0016] In a particularly preferred embodiment of the invention, the dosing device can be trained by optimizing the opening time of the closure element through iterative steps based on the fill level. This optimizes each batch in the dosing mixer by minimizing the amount of granules heated in the dryer that are present. Furthermore, this allows for the detection of changing parameters during the production process, and the batch quantity is immediately adjusted accordingly.
[0017] The sensors are conveniently equipped with a debouncing algorithm to prevent sensor signals triggered by falling plastic granules. Therefore, falling granules cannot trigger sensor signals. 1040-27087 3 28.11.2025
[0018] By eliminating this source of error, the measuring accuracy of the dosing mixer is further improved and the batch quantity supplied is more accurate.
[0019] It proves advantageous if the dosing device includes a fourth sensor in addition to the first, second, and third sensors. This allows the measuring accuracy of the dosing device to be improved even further, since the opening times then fall, for example, between the second and fourth sensors, thus achieving a shorter reaction time for controlling the closure element.
[0020] Light sensors are advantageous. They can detect the fill level particularly quickly and accurately. This allows the closure element to be opened or closed almost in real time. Consequently, control inertia, which can lead to a delayed opening or closing of the closure element, is largely prevented.
[0021] It is also advantageous if the slide gate is a knife gate. A knife gate precisely "cuts off" the stream of granules leaving the dryer, thus increasing the accuracy of the measured granule quantity.
[0022] Another aspect of the invention relates to a feeding device for feeding an injection molding machine, which includes the metering device described above. For the reasons mentioned above, such a feeding device has a much lower heat loss than known feeding devices, which, in comparison, exhibit a significant waste of heat due to the granules placed in the tube.
[0023] Another aspect of the invention relates to a method for dosing plastic granules from a dryer into a dosing mixer of an injection molding machine, comprising the process steps of detecting the fill level of the plastic granules in the dosing mixer with a plurality of sensors arranged at different heights in the dosing mixer, opening a controllable closure element which can close and release an outlet of the dryer into the pipe depending on the fill level of the plastic granules in the dosing mixer, and closing the closure element depending on the fill level of the plastic granules in the dosing mixer. This ensures that precisely the amount of granules required for one injection molding cycle is supplied to the dosing mixer as needed.
[0024] In a further particularly preferred embodiment of the invention, the dosing device is calibrated by providing a first sensor for a low fill level, a second sensor for a high fill level, and a third sensor for a full fill level, and a control device that opens and closes the closure element triggered by sensor signals. This calibrating function allows the dosing device to be adapted to any feeding device, whether existing or new. The dosing device can also be adapted to changing operating parameters at any time, so that after calibrating the dosing device, the amount of granules is adjusted to the quantity processed in one cycle of the injection molding machine.
[0025] It is preferred that the first sensor sends an opening signal to the control device when the fill level is below the first sensor.
[0026] It is preferred that the second sensor sends a closure signal to the control device when the fill level is equal to or above the level of the second sensor.
[0027] Preferably, the third sensor sends a closing signal to the control unit when the fill level is equal to or above the level of the third sensor. The control unit processes these three sensor signals to determine the opening duration of the closing element, ensuring that the fill level in the metering mixer stabilizes between the levels of the second and third sensors. This may require one or more correction iterations.
[0028] At the beginning of the teaching process for the dosing device, it is preferred to measure the time interval between the signal of the first and second sensor, thereby determining an initial opening time t. openi is defined. This is a good starting value, as the amount of granules filled into the dosing mixer usually has a fill level that lies within the target range between the second and third sensors.
[0029] The invention is also preferably characterized by the fact that a second opening time t op en2 through a first correction time t cor ri is estimated if at t op eni also sends a closure signal and t ope n2 is defined as t op en2= t op eni- t cor ri . This iteration step brings the fill level of the granules into the desired range between the second and third sensors.
[0030] It is preferred if, in the event that at t open 2. The second and third sensors send a shutter signal, a second correction time t corr2 is determined, which is defined as tcorr2=(tFuii-tHigh) / 2, where tpuii is defined as the time from the opening of the closure element until the closure signal of the third sensor, and tnigh is defined as the time from the opening of the closure element until the closure signal of the second sensor. This second iteration step (1040-27087 5 28.11.2025) is performed if the third sensor is still sending a closure signal after the first iteration step. This ensures that the fill level is iterated between the second and third sensors at least once.
[0031] In another preferred embodiment of the invention, in the case that the fill level after t opIf the fill level is lower than the low level indicated by the first sensor, an alarm is triggered and the sealing element remains open. This prevents the dosing mixer from being underfilled with granules, which also helps to ensure that the granule fill level is brought within the target range.
[0032] In a further particularly preferred embodiment of the invention, t op The system recalculates the required amount of granules each time the dosing mixer is filled to compensate for any loss of granules from the mixer to the injection molding machine during the filling process. This control step compensates for an undesirable, but unavoidable, overlap between the filling of the dosing machine and the injection molding machine.
[0033] Further advantages and features will become apparent from the following description of an exemplary embodiment of the invention with reference to the schematic diagrams. These are shown in a representation not to scale:
[0034] Figure 1: a schematic view of a feeding device for filling an injection molding machine comprising a metering device and a metering mixer
[0035] Figure 2: a perspective view of the dosing mixer and
[0036] Figure 3: a level-time diagram to illustrate the control strategy of the dosing device.
[0037] Figure 1 shows a feeding device, collectively designated by reference numeral 11. The feeding device 11 serves to feed an injection molding machine 13. The feeding device 11 comprises a dryer 15, a metering mixer 17, a pipe 19 connecting the dryer 15 to the metering mixer 17, and a metering device 21. The metering mixer 17 is also shown in Figure 2. 1040-27087 6 28.11.2025
[0038] The dryer 15 dries plastic granules or powder, which are processed into injection-molded parts in the injection molding machine 13. Drying the plastic material is particularly advantageous for hygroscopic plastics. Hereinafter, the plastic material to be injection-molded is referred to collectively as granules.
[0039] In the dryer 15, the granules are heated to up to 180 °C. The dried granules pass through the pipe 19 into the metering mixer 17 and are then conveyed from there to the injection molding machine 13. The metering mixer 17 homogenizes the granules and delivers the required quantity of granules to the injection molding machine 13. A closing element in the form of a slide 23 is located below an outlet 25 of the dryer 15. The slide 23 opens or closes the outlet 25, allowing dried granules to be fed into the metering mixer 17. Typically, the granules remain in the pipe 19 until they are processed in the injection molding machine 13 and cool down accordingly. According to the prior art, the pipe 19 is usually completely full at all times because the slide 23 is permanently open.In the injection molding machine 13, the granules cooled in the tube 19 must be reheated from a temperature of less than 180 °C in order to be melted.
[0040] This energy waste can be largely prevented by the dosing device 21. Figure 1 shows that the dosing device 21 comprises a first, second, and third sensor, 27, 29, 31. Figure 2 shows a fourth sensor 33, which increases the measurement accuracy. The sensors 27, 29, 31, 33 are positioned at different heights on the dosing mixer and accordingly measure different fill levels of granules in the dosing mixer 17. The first sensor 27 indicates a low fill level of granules, the second sensor 29 a high fill level, and the third sensor 31 a full fill level. The fourth sensor 33 is arranged between the first and second sensors 27, 29, thereby improving the measurement accuracy in the low fill level range. Preferably the sensors 27, 29, 31, 33 are light sensors which detect whether or not granules are present in the horizontal plane in which they are arranged.
[0041] Sensors 27, 29, 31, and 33 transmit their measurement signals to a control unit 35. The control unit 35 regulates the slide gate 23 based on the sensor signals. To ensure that the quantity of granules correlates as closely as possible with the corresponding opening time, it is preferred that the slide gate 23 be a knife gate. Sensors 1040-27087 7 28.11.2025
[0042] Sensors 27, 29, 31 and 33 are equipped with a debouncing algorithm to prevent sensor signals triggered by falling granules as they pass sensors 27, 29, 31 and 33.
[0043] The purpose of the dosing device 21 is to ensure that preferably only the quantity of granules required by the injection molding machine 13 for the next injection molding cycle is present in the dosing mixer 17. This minimizes granule cooling. Whenever this required quantity of granules is no longer present in the dosing mixer 17, the required batch of granules is fed from the dryer 15 into the dosing device 21 via the dosing device 21. For this to work, the dosing device 21 must be continuously calibrated to achieve the most optimized batch quantity. This requires determining the batch quantity based on the opening time of the slide 23, and not solely on the fill level. Therefore, the slide 23 is controlled by the control unit 35 precisely according to the granule demand.
[0044] The control process works as follows: The first sensor 27 sends an open signal to the control unit 35 when the fill level in the metering mixer 17 is below the level of the first sensor 27. The second sensor 29 sends a close signal to the control unit 35 when the fill level is equal to or above the level of the second sensor 31. The third sensor 31 sends a close signal to the control unit 35 when the fill level is equal to or above the level of the third sensor 31. If the fourth sensor 33 is provided on the metering mixer 17, it measures a low fill level, and the first sensor 27 sends a signal when the metering mixer is empty. By providing the first and fourth sensors 27 and 33, not only is the measurement accuracy increased, but it also reliably prevents the metering mixer from running dry: If the fourth sensor 33 fails, the first sensor 27 causes the slide 23 to be forcibly opened.
[0045] At the start of the learning process, the first sensor 27 sends an opening signal to the control unit 35, and the slide 35 opens. This allows granules to fall through the pipe 19 into the dosing mixer 17. When the second sensor sends a closing signal, the slide 23 closes. The time between the signals from the first and second sensors 27 and 29 is measured, and an initial opening time t is recorded. op eni is defined. If, after topeni, the closing signal of the third sensor 31 is also triggered, then t openi too long and consequently too much granule enters the dosing mixer 17. t openi Therefore, a correction time t is required. cor ri can be reduced. t cor ri is estimated in a first iteration step. 1040-27087 8 28.11.2025 This results in t op en2= topeni- t CO rri- If at t ope n2 the shutter signal of the third sensor 31 was no longer triggered, then t open2 be maintained and the batch quantity in the dosing mixer is acceptable 17.
[0046] If after t open 2. If the shutter signal of the third sensor 31 is still triggered, then a further iteration step with a further correction time tc is required. Or r2 is necessary. Here, tpuii is defined as the time from the opening of the slide 23 until the closing signal of the third sensor 31, and tnigh is defined as the time from the opening of the slide 23 until the closing signal of the second sensor 29. Then, an average value for t is calculated. cor r2 defines: t CO iT2=(tFuii-tHigh) / 2. If the closing signal of the third sensor 31 is not triggered after this iteration step, then a new estimated correction time t is used in the next filling step of the dosing mixer. cor The iteration has begun, in which the dosing device 21 is re-learned or t open 2 will be newly determined.
[0047] The described iteration steps are visualized in a "level-time diagram" in Figure 3. This diagram shows that the goal of the iteration is to control the slide valve 23 in such a way that the level is maintained or stabilizes in the area between the second sensor 29 and the third sensor 31.
[0048] In the event that the fill level changes after t openi If the fill level is lower than the low level of the first sensor 27, an alarm is triggered and the slide 23 remains open. This prevents the dosing mixer 17 from emptying completely and ensures it is never underfilled.
[0049] It is possible that during the filling of the dosing mixer 17, the required batch quantity is simultaneously dispensed from the dosing mixer 17 to the injection molding machine 13, causing the slide 23 to remain open for too long and too much granulate to be dispensed into the dosing mixer 17. Therefore, to peniThe value is recalculated every time the dosing mixer is filled, in order to correct this inaccuracy.
[0050] The dosing device 17 is extremely flexible and can be quickly retrofitted to existing feeding devices 11 or be a component of a new feeding device. 1040-27087 9 28.11.2025
[0051] Legend:
[0052] 11 Feeding device
[0053] 13 injection molding machine
[0054] 15 dryers
[0055] 17 metering mixers
[0056] 19 pipe
[0057] 21 Dosing device
[0058] 23 Locking element, slider
[0059] 25 Dryer outlet
[0060] 27 First sensor
[0061] 29 Second sensor
[0062] 31 Third Sensor
[0063] 33 Fourth Sensor
[0064] 35 Control device
Claims
1040-27087 10 28.11.2025 1. Metering device (21) for metering plastic granules from a dryer (15) into a metering mixer (17), which metering mixer (17) is intended for filling an injection molding machine (13), wherein the dryer (15) can be connected to the metering mixer (17) by a pipe (19), further characterized by a controllable closing element (23), in particular a slide (23), which can close and release an outlet (25) of the dryer (15) into the pipe (19), a plurality of sensors (27, 29, 31, 33), which can detect different granule fill levels in the metering mixer (17) and can generate corresponding sensor signals and - a control device (35) which can open and close the locking element (23) depending on the sensor signals.
2. Dosing device according to claim 1 characterized in that a first, second and third sensor (27, 29, 31) can be arranged at such a height on the dosing mixer (17) that they can detect a low, a high and a full fill state.
3. Dosing device according to claim 1 or 2 characterized in that the dosing device (21) can be trained by optimizing the filling level with respect to the opening duration of the closure element (23) through iterative steps.
4. Dosing device according to one of the preceding claims, characterized in that the sensors (27, 29, 31, 33) are equipped with a debouncing algorithm to prevent sensor signals triggered by falling plastic granules.
5. Dosing device according to one of claims 2 to 4, characterized in that the dosing device (21) comprises a fourth sensor (33) in addition to the first, second and third sensor (27, 29, 31).
6. Dosing device according to one of the preceding claims, characterized in that the sensors are light sensors (27, 29, 31, 33). 1040-27087 11 28.11.2025 7. Metering device according to one of the preceding claims, characterized in that the slide is a knife slide (23).
8. Feeding device (11) for feeding an injection molding machine (13) comprising - a dryer (15), - a dosing mixer (17), - a pipe (19) which connects the dryer (15) to the dosing mixer (17) and - a metering device (21) according to one of the preceding claims.
9. Method for dosing plastic granules from a dryer (15) into a dosing mixer (17) which fills an injection molding machine (13), comprising the following process steps: - Detecting the fill level of the plastic granules in the dosing mixer (17) with a plurality of sensors (27, 29, 31, 33) which are arranged at different heights in the dosing mixer (17), - Opening of a controllable closure element (23), in particular a slide (23), which can close and release an outlet (25) of the dryer (15) into the pipe (19), depending on the fill level of the plastic granules in the dosing mixer (17) and - Closing of the closure element (23) depending on the fill level of the plastic granules in the dosing mixer (17).
10. Method according to claim 9, characterized in that the dosing device (21) is trained by providing a first sensor (27) for a low fill level, a second sensor (29) for a high fill level and a third sensor (31) for a full fill level and a control device (35) which opens and closes the closure element (23) triggered by sensor signals.
11. Method according to claim 10, characterized in that the first sensor (27) sends an opening signal to the control device (35) when the fill level is below the first sensor (27).
12. Method according to claim 10 or 11, characterized in that the second sensor (29) sends a closure signal to the control device (35) when the fill level is equal to or above the second sensor (29). 1040-27087 12 28.11.2025 13. Method according to claim 11 or 12, characterized in that the third sensor (31) sends a closure signal to the control device (35) when the fill level is equal to or above the third sensor (31).
14. Method according to claim 11 and 12 or according to claim 11 and 13, characterized in that the time interval between the signal of the first and second sensor (27, 29) is measured, thereby determining a first opening time t op eni is defined.
15. Method according to claim 14, characterized in that a second opening time t op en2 through a first correction time t cor ri is estimated if at t op eni also the third sensor (31) sends a closure signal and t open 2 is defined as topen2 — topeni" tcorri - 16. Method according to claim 15, characterized in that in the case that at t 0Pen2 the second and third sensors (29,31) send a shutter signal, a second correction time tc Or r2 is determined, which is defined as t C orr2=(tFuii-tHigh) / 2, where tpuii is defined as the time from opening the locking element (23) to the locking signal of the third sensor (31) and tnigh is defined as the time from opening the locking element (23) to the locking signal of the second sensor (29).
17. Method according to one of claims 14 to 16, characterized in that in the event that the fill level changes after t ope If the level of the first sensor (27) is less than the low level, an alarm is triggered and the locking element (23) remains open or is opened.
18. Method according to one of claims 14 to 17, characterized in that topeni is recalculated each time the metering mixer (17) is filled in order to correct for the removal of plastic granules from the metering mixer (17) into the injection molding machine (13) during the filling of the metering mixer (17).