Injection molding machine

Abstract

Injection molding machine with a hydraulic drive unit (1), with: - a piston that can be moved hydraulically between two end positions (E1, E2) in a cylinder (2) for moving an injection molding machine part, - a hydraulic pump (4) for pumping hydraulic fluid, - a hydraulic line (5) between hydraulic pump (4) and cylinder (2) and - a control or regulating unit (7) for controlling or regulating the hydraulic pump (4) via control signals, - a measuring device for measuring the flow volume (Q) of the hydraulic fluid per unit of time (t) and forwarding a corresponding signal to the control unit (7), which calculates the position (P) of the piston from this, characterized in that the measuring device is part of the hydraulic pump (4) or part of a valve (6) arranged in the hydraulic line (5), which valve (6) itself is designed to measure the flow volume (Q) of the hydraulic fluid in the hydraulic line (5) per unit of time (t), wherein the control unit (7) controls the valve (6) or the hydraulic pump (4) based on stored target profiles with a target pressure value (p). soll ) and / or a volume flow setpoint (Q soll ) controls and thus controls or regulates the volume flow (Q) and / or the hydraulic pressure (p) in the hydraulic line (5) after the hydraulic pump (4) or after the valve (6) up to the cylinder (2).

Description

[0001] The invention relates to an injection molding machine with a hydraulic drive unit, a piston hydraulically movable between two end positions in a cylinder for moving an injection molding machine part, a hydraulic pump for conveying hydraulic fluid, a hydraulic line between the hydraulic pump and the cylinder, and a control or regulating unit for controlling or regulating the hydraulic pump (and optionally a valve).

[0002] Hydraulically driven movements are performed in various areas and components of an injection molding machine. For example, such drive units are used for core pulls, ejectors, mounting plates, and similar components. These typically involve the translational movement of a piston within a cylinder, achieved by supplying hydraulic fluid to a specific section of the cylinder. A key aspect of these hydraulic drive units is the ability to precisely control the piston's movement and position throughout the entire hydraulic system. This ensures that each injection molding cycle is executed accurately, smoothly, and energy-efficiently. The control unit then uses data acquired during the injection molding cycle to regulate and control the hydraulic flow rates of the hydraulic pump and any valves present.

[0003] To determine the most accurate possible position of the piston in the cylinder, an electrohydraulic control arrangement with an adjustable fluid pump and a variable-speed electric drive for an injection molding machine is known, for example, from DE 10 2007 007 005 A1. In this arrangement, the piston position is deduced from data acquired by a displacement measuring system. Based on this measured value, certain control variables and the required amount of hydraulic fluid for the individual phases of an injection molding process are then calculated.

[0004] Similarly, a hydraulic control device for the injection cylinder of a plastic injection molding machine with an electromechanical displacement measuring system is known in DE 34 04 927 A1.

[0005] DE 32 13 623 A1 discloses a control system for hydraulic drives which includes a volume sensor and controls the hydraulic flow via a proportional valve. DE 32 09 313 also discloses a program control system for hydraulic drives in which a volume sensor emits electrical pulses for discrete sub-quantities of the hydraulic medium and a position setpoint transmitter controls a proportional valve.

[0006] In DE 10 2008 010 703 A1 such a displacement measuring system for recording the position of a piston of a piston-cylinder unit is known in detail.

[0007] A disadvantage of such hydraulic drive units is that displacement measuring systems require a relatively large amount of space in the area of ​​an injection molding machine, have separate connections and wiring, and must be integrated into the overall control system.

[0008] A hydraulic drive unit according to the preamble of claim 1 is known from WO 01 / 66957 A2. This prior publication describes a passive measuring arrangement.

[0009] The unpublished German patent application DE 20 2011 002 591 U1 discloses a hydraulic drive unit, but without a piston movable in a cylinder. A hydraulic device with a control pump is known from German patent application DE 43 35 403 C1.

[0010] The object of the invention is therefore to provide an injection molding machine that is improved compared to the prior art. In particular, it should be possible to dispense with a complex and cumbersome displacement measuring system for detecting the piston position – while retaining the advantages of control engineering.

[0011] This problem is solved by an injection molding machine with the features of claim 1. According to the invention, a measuring device measures the flow volume of the hydraulic fluid per unit of time (in the hydraulic line or at the beginning of the hydraulic line) and transmits a corresponding signal to the control unit, which then calculates the position of the piston. This allows the piston position to be deduced from the measuring device without directly, but cumbersomely, measuring the piston's position. In other words, the position of the driven piston is inferred from the flow rate of hydraulic fluid through the hydraulic line.

[0012] A first embodiment of the present invention provides that the flow volume can be measured by the measuring device using a valve arranged in the hydraulic line for adjusting the flow volume and / or the hydraulic pressure. The valve provides a signal corresponding to the actual flow volume (depending on the load pressure). If this signal is then evaluated by the control system over time during the cylinder stroke, this value consequently corresponds to the cylinder volume. That is, for example, in the case of a core pull cylinder, a reference stroke (regardless of the speed) would have to be performed once to determine the actual cylinder volume. In the control system, the actual flow rate is then converted into a displacement value, allowing the cylinders to utilize the advantages of the displacement sensors via this "quasi-actual value".

[0013] Particularly preferably, this valve may be designed in the form of a so-called pQ valve, wherein the arrangement of this pQ valve between the pump and the consumer allows both the control and regulation of the hydraulic pressure and / or the flow rate, and also measures the actual hydraulic flow rate in the outlet area of ​​the pQ valve. The pressure and flow proportional functions of valves known from the prior art can be integrated into such a pQ valve.

[0014] An advantage of this design is that no displacement sensor is required in the mold and only one valve is necessary. Additionally, hard stops of the core pull at the end position can be prevented by targeted deceleration (ramping). High pressure peaks at the core end positions can also be prevented by timely deceleration before reaching the end position. The core pulls can also be moved to intermediate stops. Furthermore, it is possible to use the cores as ejectors with profile machining, thus enabling a clean and precise transfer to a robot. These functional descriptions for the core pull are exemplary and could be used for all movements in the injection molding machine.

[0015] According to a second, alternative embodiment, the flow rate can be measured by the hydraulic pump using the measuring device. Thus, the pQ valve is not used (and can therefore be omitted); instead, the flow rate is measured via the pump's swivel angle. The hydraulic pump provides a signal corresponding to the current pump flow rate. Similar to the pQ valve evaluation, this signal is analyzed over time in the control unit during a cylinder stroke, resulting in the cylinder volume. A reference stroke is also required to determine the actual cylinder volume. The control unit then converts the actual flow rate into a displacement value, allowing the cylinders to utilize the advantages of the displacement sensors via this "quasi-actual value" (see also the advantages of the first embodiment).

[0016] The additional advantages of this measurement via the pump compared to the measurement via the valve lie in the cost savings, since no valve is needed anymore, and the fact that the measurement variant can be installed and used in virtually any existing injection molding machine.

[0017] In contrast, measurement via the valve has the advantages over measurement via the pump that parallel movements of several cylinders (systems) are possible and that the measurement becomes more accurate due to the shorter remaining length of the hydraulic line from the valve to the cylinder.

[0018] Both of the aforementioned variants can include a learning function. This learning function gradually improves accuracy. The actual displacement value (=pump flow rate) measured during the calibration process is measured again during normal operation and corrected. This process can be configured to be performed once or cyclically. Instead of calibration, the cylinder volume for both directions could be entered. A subsequent learning function then refines this setting. It is also possible to enter the cylinder data (stroke, rod and piston diameter) as parameters into the control unit. The cylinder volume for both directions is then calculated from this data. Here, too, a subsequent learning function can refine the settings.

[0019] It is also conceivable to eliminate the limit switches for the cylinder end positions in the tool, since the cylinder's position is always available due to the continuous volume calculation. The end position during a calibration process would then be detected by the actual volume flow value being 0. This method is also applicable for end position detection of the cylinder.

[0020] Furthermore, custom characteristic curves can be stored for different speed settings, which are determined in a calibration process.

[0021] In both of the aforementioned embodiments (flow rate measurement via valve or pump), the measuring device can be integrated directly into the valve or pump. For example, it could be a specific flow rate sensor or a specific swivel angle sensor, from whose acquired data the flow rate can then be derived or calculated, taking the flow time into account.

[0022] For both design variants, the actual maximum cylinder volume, determined during a reference run, can be stored in the control unit. A flow-displacement converter adds up the flow volume transmitted by the valve at specific intervals and converts it into a piston displacement value based on the maximum cylinder volume. This flow-displacement converter can be located upstream of the control unit or be integrated into it. Crucially, the flow rate in the valve or pump is transmitted to this flow-displacement converter at regular intervals (e.g., every 6 milliseconds) by a corresponding sensor, and the total volume of hydraulic fluid delivered over a specific period is calculated by summing these values.This volume value is related to the maximum possible cylinder volume, from which the cylinder's filling volume and thus the piston's position can be calculated.

[0023] Protection is also sought for an injection molding machine with a hydraulic drive unit according to the invention.

[0024] Further details and advantages of the present invention are explained in more detail below with reference to the description of the figures and the exemplary embodiments shown in the drawings. These show: Fig. 1 a schematic representation of a state-of-the-art hydraulic drive unit, Fig. 2 a schematic representation of a first embodiment of a hydraulic drive unit according to the invention with measurement via a valve and Fig. 3 and Fig. 4 schematic representations of a second embodiment of a hydraulic drive unit according to the invention with measurement via the pump.

[0025] It should be noted that the functional descriptions mentioned below refer to a core pull of an injection molding machine, but this is only to be seen as an exemplary description, since the general function can be used for all movements of a hydraulically driven component of an injection molding machine.

[0026] In general, a hydraulic drive unit 1 can, for example, move a core pull in the area of ​​a fixed mold mounting plate 3 via a piston of a cylinder 2. A mold half 9 is arranged on this fixed mold mounting plate 3, wherein a second mold half 10 can be moved in the direction of mold half 9 via a movable mold mounting plate 11.

[0027] In standard injection molding machines, the pressure and quantity control of a moving device (cylinder 2 including piston) for injection molding machine parts is achieved via control pumps. In special cases – such as in Fig. Figure 1 shows the use of a pressure proportional valve. This allows for a separate pressure output for each injection molding machine component (e.g., a core pull) via a screen, even when multiple core pulls are operated in parallel.

[0028] Furthermore, a proportional flow valve can optionally be used, allowing individual core pulls to be operated in parallel at different speeds. The positioning of the individual core pulls, or rather the cylinders 2 of the core pulls, is controlled by limit switches or – as in the illustrated case – by [method not specified]. Fig. 1 - via displacement sensors 8. However, these displacement sensors 8 have a relatively high space requirement, require separate and relatively cumbersome integration into the control system, and are cost-intensive.

[0029] Generally, a hydraulic pump 4 (with an upstream motor, not shown) is controlled or regulated by a control unit 7 via control signals S. Additionally, a pressure setpoint p is specified by this control unit based on stored target profiles. soll and a volume flow setpoint Q soll to the valve 6, whereby the control or regulating unit 7 controls or regulates the volume flow Q and the hydraulic pressure p in the hydraulic line 5 after the pump 4 or after the valve 6 up to the consumer (cylinder 2).

[0030] In the state of the art (see Fig. 1) The position P of the piston 12 of the cylinder 2, changed by the supplied hydraulic fluid, is detected by a displacement sensor 8 and expressed as a displacement value. ist output to the control or regulating unit 7.

[0031] In contrast, according to a first embodiment of the invention - see Fig. 2 - the flow volume Q of the hydraulic fluid in the hydraulic line 5 per unit of time t is measured by the valve 6 itself and a corresponding signal is forwarded to the control or regulation unit 7 or a quantity-distance converter Qs, which calculates the position P of the piston 12 of the cylinder 2 and sends a corresponding distance signal. ist the control unit 7. Accordingly, the measuring device is part of the valve 6. The quantity-displacement converter Qs thus indirectly determines the cylinder volume V via the valve 6. This provides the control unit 7 with a displacement value. istavailable, which corresponds to the position P of the piston 12 between the end positions E1 and E2 - without using a displacement sensor 8.

[0032] As from Fig. As can be seen in Figure 3, according to this second embodiment of the invention, a valve 6 is no longer necessary. Instead, the pump 4 itself serves to measure the flow volume Q. ist through pump 4 and consequently through hydraulic line 5. The measuring device is therefore part of pump 4. The hydraulic pressure p can also be measured. ist These measured values ​​Q ist and p ist are then supplied to the control unit 7, whereby a quantity-distance converter Qs of the control unit can thus indirectly be used to deduce the cylinder volume V via the pump 4.

[0033] In Fig. Figure 4 further illustrates how characteristic curves stored in a memory by the control unit are used to output a setpoint pressure p. soll and / or a volume flow setpoint Q soll can be used as a basis for calculation and control of pump 4.

[0034] Through this hydraulic drive unit 1 according to the invention Fig. 2, Fig. 3 and Fig. 4. The advantages of a displacement sensor 8 can be utilized without actually using it. Thus, as an advantage over the prior art, either only a valve 6, for example in the form of a pQ valve, or even just the pump 4 is required. By supplying the displacement value, the displacement can be... istHard impacts of the core pull at the end position can be prevented (for example, by targeted braking). Additionally, the cylinder pistons can be stopped in various intermediate positions. Furthermore, high pressure peaks at the core end positions can be prevented by timely braking. With cores used as ejectors with profile machining, a clean transfer to a robot is possible.

[0035] A further advantage of the present invention is that the flow volume Q can be determined independently of the load pressure. It is also advantageous that a reference stroke (regardless of speed) can be performed in a calibration cycle to determine the actual cylinder volume V. This new system can also be easily retrofitted to existing injection molding machines, since the oil quantity (volume flow Q) is proportional to the piston's position P.

[0036] Thus, the present invention presents an improved hydraulic drive unit 1 in which the piston position P of a consumer 2 can be deduced from the flow rate Q of hydraulic fluid through a hydraulic line 5 measured by a measuring device, and this value serves as the basis for the control unit to calculate the flow volume Q and / or the hydraulic pressure p in the valve 6 or in the hydraulic pump 4. The measuring device used either measurement signals from the valve 6 or the pump 4 to determine the flow rate Q.

Claims

[1] Injection moulding machine with a hydraulic drive unit (1), with: - a piston hydraulically movable between two end positions (E1, E2) in a cylinder (2) for moving an injection moulding machine part, - a hydraulic pump (4) for pumping hydraulic fluid, - a hydraulic line (5) between hydraulic pump (4) and cylinder (2) and - a control or regulating unit (7) for controlling or regulating the hydraulic pump (4) via control signals, - a measuring device for measuring the flow volume (Q) of the hydraulic fluid per unit of time (t) and transmitting a corresponding signal to the control or regulating unit (7), which calculates the position (P) of the piston therefrom, characterized bythat the measuring device is part of the hydraulic pump (4) or part of a valve (6) arranged in the hydraulic line (5), which valve (6) itself is designed to measure the flow volume (Q) of the hydraulic fluid in the hydraulic line (5) per unit of time (t), wherein the control or regulating unit (7) controls the valve (6) or the hydraulic pump (4) based on stored target profiles with a pressure target value (p soll ) and / or a volume flow setpoint (Q soll ) and thus controls or regulates the volume flow (Q) and / or the hydraulic pressure (p) in the hydraulic line (5) after the hydraulic pump (4) or after the valve (6) up to the cylinder (2). [2] Injection molding machine according to claim 1, characterized bythat the actual maximum cylinder volume (V) that can be determined in a reference run is stored in the control or regulating unit (7), wherein a quantity-distance converter (Qs) adds the flow volume (Q) transmitted by the measuring device at certain time intervals (t) and converts it into a distance value (distance ist ) of the piston. [3] Injection moulding machine according to claim 1 or 2, characterized by that the flow volume (Q) can be measured by the measuring device using the hydraulic pump (4). [4] Injection moulding machine according to claim 1 or 2, characterized by that the flow volume (Q) can be measured by the measuring device by means of a valve (6) arranged in the hydraulic line (5) for adjusting the flow volume (Q) and / or the hydraulic pressure (p). [5] Injection molding machine according to claim 4, characterized bythat the valve (6) can be controlled or regulated by the control or regulating unit (7).

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