DE19619860A1 - Injection piston movement control - Google Patents

Abstract

To control the movement of a working piston (9) for the injection unit (6) of an injection or pressure moulding machine, a constant min. flow of hydraulic fluid is maintained during the movement at different speeds and also during the further pressure phase. The total vol. of hydraulic fluid available is varied to maintain the min. flow and also any additional hydraulic flows required for control purposes. Also claimed is an appts. with an additional fluid opening with the channel (27) for the supply (17,21,22) in operation, to maintain a constant min. flow.

Description

The invention relates to a method according to the The preamble of claim 1 and a device according to the preamble of claim 3.

If there is talk of "regulating" in this context, then so is intended to express that it is not in the invention it depends whether it is a control or a re act in the narrower sense of these terms, rather both are included. Since the invention also in the first Li never concerned with the drive piston, it is also not significant Lich whether it is now the hydraulic fluid Driving piston of an injection or die casting machine acts. Because in any case it is about a so-called "Shot" with a predetermined, desired path, pressure or Perform speed profile.

Methods and devices of this type are numerous Embodiments have been proposed, just one example be referred to US-A-4,610,831. All known Solutions is common that the drive cylinder just like that much hydraulic fluid is supplied than one to carry out the movement needed.

Now such drives have been strong in recent years Upswing with improvements in accuracy and approach speed of speech. Ultimately surrendered there are always limits to the development opportunities that arise Properties of the respective system, such as inertia and accuracy the same.

The applicant has carried out intensive investigations into the  factors determining these limits and doing so found that the known drive systems u. a. a certain Hysteresis in their response behavior, an Er appearance, that of the desired speed and accuracy of the response behavior stands in the way.

The present invention is therefore based on the object the response behavior of a drive for the injection process to improve injection and die casting machines and esp in particular to switch off a hysteresis if possible. This succeeds in a surprising way by the characteristic features of the Claims 1 and 3 respectively.

This solution is surprising because it is one hand is extremely easy to implement, and on the other hand, because a So far expert could probably assume that such a ger constant flow of hydraulic fluid except an additional energy expenditure brings nothing. In fact it has shown in experiments that by such a simple measure the hysteresis when the system responds largely to fully constantly switched off and thus the speed and accuracy responsiveness can be increased.

It is entirely possible in the context of the invention that both the constant minimum flow of the hydraulic fluid and also the current additionally supplied for control purposes Control and / or regulation are subjected. Since it is but in the former by a "minimal flow", i.e. H. so by one very low compared to the current used for control purposes Flow rate, it is understood that the Change of the minimal flow in general only a little We kung, which is why the procedure according to claim 2 be is preferred. It should be mentioned that this is not always the case len must be so, rather it may be desirable can, the minimum flow z. B. periodically change to normal movement overlay a slight tremor, the more friction-related peculiarities of the response behavior turn off, and or the ways that this minimal flow undergoes some kind of self-cleaning effect.  

The invention is best illustrated by a device with the Features of claim 3 realized. According to the However, the above explanations are a training according to claim 4 preferred, not least because it also changes the design effort is simplified.

Further details of the invention are based on the following description of schematically with reference to the drawing illustrated embodiments illustrated. It shows gene:

Fig. 1 is an inventive hydraulic scheme for a die casting machine, whereas the

Fig. 2 to 4 illustrate variants.

According to Fig. 1 is Darge provides a die of a die casting machine not shown in detail, formed of a fixed mold half 1 and a movable mold half 2, which together define a mold cavity 3. A casting sleeve 4 is fastened to the fixed mold half 1 , into which metal can be filled in a known manner via a filling opening 5 and can be shot into the mold cavity 3 by means of an injection element in the form of a casting piston 6 .

When talking about a casting piston as an injection device is understood by those skilled in the relevant Technology that as an injection device for injection molding machines in general lengthwise movable and rotatable screws in Question come up, although use in this area too of pistons is known per se.

The casting piston 6 is connected to a piston rod 7 , which is connected via a coupling 8 to the piston rod of a drive piston 9 in a drive cylinder 10 . The control for this drive piston is only shown in simplified form in FIG. 1 insofar as this is necessary for an understanding of the present invention.

Thereafter, the drive piston 9 (based on FIG. 1) is moved to the left by supplying hydraulic fluid via a first line or inlet opening 11 for the cylinder 10 , whereas the drive piston 9 (and thus also the injection element 6 ) is moved to the right The supply of hydraulic fluid is carried out via a second line or opening 12 at the opposite end of the drive cylinder 10 . The control of the line 12 is done in a conventional manner known per se, ie essentially via a control valve 13 which is switched in synchronism with the valves controlling the line 11 such that the line 12 either (as shown) with a supply line 14 and Via a check valve 15 is connected to a pump 16 , which receives hydraulic fluid from a storage tank 17 ; or the line 12 is connected to a drain line 18 which, when the drive piston moves to the left (seen in FIG. 1), allows the hydraulic fluid on the left side of the drive cylinder 10 to flow out via a throttle valve 19 .

The movement of the drive piston 9 to the right is controlled in a manner known per se by a proportional valve 20 which has three positions, namely for a left movement, a right movement and for standstill. Here, a particular path through the proportional valve 20 and / or Geschwin is impressed digkeitsprofil as technology in the relevant technology is known. The supply of hydraulic fluid takes place from a pressure storage unit 21 , which receives hydraulic fluid from the tank 17 via a line 23 and a check valve 24 from a further pump 22 , a switching valve 25 ensuring a corresponding switching of the supply to the pressure storage unit 21 as well Proportional valve 20 . This latter connects in the case of a movement of the drive piston 9 to the right the line 11 with a drain line 26 which leads to the tank 17 .

Because of the tight closure of the individual chambers and passages of the valve 20 between the valve body and the Ventilge housing when closing one of the ways for the hydraulic valves within the proportional valve, a certain overlap is required to complete the other way. But this necessarily brings with it a certain hy steresis in the control behavior of the valves, which ultimately leads to a response delay and thus to a slowdown in the control behavior. But with modern machines in particular, the fastest possible reaction to the respective situation is desirable. So far, one has simply come to terms with the inevitably resulting hysteresis; in any case, the applicant is not even aware of an approach to solving this problem, even if only in the knowledge that there is a factor influencing the control time constant.

It has now been found a way in which not only the hysteresis problem can be solved, but also other advantages result in a simple manner. For this purpose, a line 27 is provided, which maintains a constant minimum flow of the hydraulic fluid during the movement of the drive piston 9 within the drive cylinder 10 at different speeds. For one thing, it is not necessary to design all control edges of the proportional valve 20 in such a way that there is a certain overlap of the edges of the valve body and of the housing on all edges, because a certain "leakage current" is permitted. However, this largely eliminates hysteresis and improves the response behavior of valve 20 .

But not only the object of the invention, namely a rapid response of the valve is solved; In addition, at least one of the control edges of the valve 20 has to be machined less precisely, so that an inexpensive res valve 20 also results. In addition, the compressibility of the hydraulic fluid was pointed out variously in the literature (cf. EP-A-0 097 275), which is certainly due at least in part to gas inclusions and their behavior when the valves suddenly switched. However, since according to the invention the flow of the hydraulic fluid is not completely shut off, this problem is also alleviated.

As can be seen, the line 27 has a throttle opening 28 . Their arrangement is in itself irrelevant, ie it can (as shown) within the course of the line 27 or at the beginning or end, z. B. also be provided directly on the cylinder 10 . In itself, it is sufficient if this opening has an unchangeable flow cross-section, especially since a change of the same because of the small flow rates is of little importance for the control of the piston 9 . In this respect, the control is simplified if only the current supplied for re gel purposes via the valve 20 (in addition to the flow through line 27 ) is changed.

If we are talking of "low flow rates", it should be mentioned that the proportion of this flow is not very critical, but that it is kept as low as possible for reasons of efficiency. In practice, it depends on whether the flow or its ratio to the control current via the valve 20 is measured during the movement of the piston 9 or in its actual standstill during the holding pressure phase. During the movement of the piston 9 , depending on the speed, a ratio of the current through the line 27 to the current via the valve 20 will be in the order of 1: 40-90. This ratio increases during the holding pressure phase due to the reduced flow rates through the valve 20 and due to the increased pressure to 1: 0.5 to 1.5.

One way of influencing the opening cross section of the throttle opening 28 could be to overlay the normal control or regulation (the sensors required for this are known per se and therefore not explained in more detail here) by a slight tremor movement by periodic opening and closing of the throttle opening. This only requires a small amount of effort, but can lead to the fact that when the piston 9 is not at rest, the (higher) static friction with respect to the wall of the cylinder 10 is effective, but rather the (smaller) dynamic friction, which also accelerates the response behavior the regulation or control can contribute.

In addition, this can also have an influence on the introduction of the molding material (in die casting: liquid metal; in injection molding: molten plastic) into the mold cavity 3 in the sense of greater compression.

Although the invention has been described with reference to FIG. 1 with reference to a particular exemplary embodiment, it should now be shown with reference to FIGS. 2 to 4 that there are numerous modifications to this within the scope of the invention. Thus, FIG. 2 shows an embodiment in which the proportional valve 20 is provided in shunt to the cylinder 10. In this way, the valve 25 is immediately upstream of the cylinder 10 , its other functions being the same as those in FIG. 1. Likewise, the wiring of line 12 can remain the same as that of FIG. 1.

An essential difference to the embodiment of Fig. 1 is that the line 27 corresponding line 127 branches off at the left end of the cylinder 10 from the by-pass line 29 , but here is connected to a drain line 30 . It should be noted that this could also be the case analogously in the embodiment according to FIG. 1 by the right end of the line 27 being connected to the drain line 26 .

Fig. 3 shows the case that the proportional valve 20 is attached to the left end of the cylinder 10 and regulates the discharge during the shot. In this case too, the bypass line 227 can be connected to the drain line 18 , while its upper end (in FIG. 1) branches off from the line 12 . The pump is (similar to FIG. 1) connected to an inflow line 114 . The right of the cylinder 10 can be wired as shown in FIG. 2.

It should be mentioned that parts of the same functions in the ver different figures the same reference numerals, if necessary but with the addition of a hundred digit.

A particularly preferred embodiment is shown in FIG. 4. It is essentially similar to the embodiment according to FIG. 3, but with the difference that the line 227 connects the lines 12 and 114 to one another. The remaining circuitry is essentially the same as that of FIG. 3.

It goes without saying that, in the context of the invention, instead of a single regulating valve 20 , a plurality or a more complicated regulating or control circuit could also be used.

Claims (8)

1. A method for regulating the movement bens (9) castor an Antriebskol for the injection member (6) of an injection molding or pressure to which (9) is imparted a reciprocating movement at different speeds by means of the moving of a supplied or discharged hydraulic fluid drive piston, characterized in that during the movement at different speeds as well as during the holding phase a constant minimum flow of the hydraulic fluid is maintained and the constant minimum flow as well as an additional current supplied for control purposes comprehensive total amount of hydraulic fluid for regulating the movement is changed ver. 2. The method according to claim 1, characterized in that of the total quantity only the additional quantity supplied for control purposes Electricity is changed. 3. Device for performing the method according to claim 1, with a with an injection member ( 6 ) of an injection or die casting machine connected drive piston ( 9 ) in a with a first fluid opening ( 11 ) at one end and a second fluid opening ( 12 ) at the other End provided drive cylinder ( 10 ) and with a line system for supplying or discharging hydraulic fluid from or to a fluid source, in which line system at least one regulating member ( 20 ) is provided, characterized in that a further fluid opening with one in operation the source ( 17 , 21 , 22 ) connected line ( 27 ; 127 ; 227 ) is provided for maintaining a constant minimum flow of hydraulic fluid. 4. The device according to claim 3, characterized in that the operation connected to the source ( 17 , 21 , 22 ) Lei device ( 27 ; 127 ; 227 ) bypasses at least one regulating member ( 20 ), expediently all organs adjustable for regulating purposes. 5. The device according to claim 4, characterized in that the line ( 27 ; 127 ; 227 ) is designed as a short or shunt line to a proportional valve ( 20 ). 6. Device according to one of claims 3 to 5, characterized in that the line (27; 127; 227) is the downstream side of the drive cylinder (10) forming the side of the drive cylinder (10) connected to the during the injection process (Figure 3. 4). 7. Device according to one of claims 3 to 6, characterized in that the line ( 27 ; 127 ; 227 ) via a wide re line ( 11 ; 114 ) of the line system with a hydraulic fluid supplying device ( 21 , 22 ), in particular a pump ( 22 ). 8. Device according to one of claims 3 to 7, characterized in that the unit of line ( 27 ; 127 ; 227 ) and further fluid opening comprises an optionally adjustable throttle cross-section ( 28 ).