GB2063516A

GB2063516A - Control means for adjusting members

Info

Publication number: GB2063516A
Application number: GB8032497A
Authority: GB
Original assignee: ENGEL KG L
Current assignee: ENGEL KG L
Priority date: 1979-10-10
Filing date: 1980-10-08
Publication date: 1981-06-03
Also published as: GB2063516B; ATA661579A; DE3037696C2; AT365118B; DE3037696A1; FR2467431B3; FR2467431A1

Abstract

A control means for adjusting members which are actuable in a multi-stage or continuous manner in plastics processing machines, comprises a reference value programmer for issuing reference values to the adjusting member, an actual value generator and an evaluation circuit which forms correction values for the adjusting member, in dependence on the reference value-actual value differences. Before the plastics processing machine is put into operation or after repairs thereon, a checking value programmer (20, 22) is triggered, for issuing a series of checking values (P1, P2 ... Pn) which are distributed over the adjustment range of the adjusting member (1). The evaluation circuit (21) forms correction values (K1, K2 ... Kn) according to the differences between the checking value and the actual value, and stores the correction values in a correction value memory (23). The adjusting values initiated by the reference value programmer (15) are corrected in accordance with the associated correction values (K1, K2 ... Kn). <IMAGE>

Description

SPECIFICATION Control means for adjusting members which are actuable in a multi-stage or continuous manner The invention relates to a control means for adjusting members which are actuable in a multistage or continuous manner, in plastics processing machines, in particular for electromagnetic proportional valves in injection moulding machines, having at least one reference value programmer for issuing reference values to an adjusting member, an actual value generator and an evaluation circuit which corrects the corresponding adjusting parameters for the adjusting member in dependence on the reference value-actual value differences.

In injection moulding machines for the production of plastics articles, a number of control operations must be performed during an operating procedure. In this respect, valves disposed in appropriate hydraulic circuits are set, in accordance with the respective requirements, for performance of the individual working phases such as plasticisation, mould closing, injection and the like. In order to produce plastics articles of uniform quality, it is necessary for example to control the mould filling operation in dependence on distance and time, with the respective values generally being determined empirically.Such values are stored in programmers which then apply a series of reference values to a hydraulic quantity-control valve, during the injection operation, in dependence on the distance covered by an injection screw, and, after the mould filling operation, actuate a hydraulic pressure valve in dependence on time, by means of a series of reference values. Electromagnetically controllable proportional valves are generally used for this purpose. However, a problem which arises with proportional valves of this kind is that the manufacturing inaccuracies and various other limiting conditions mean that there is not a strictly linearly proportional relationship between the adjusting parameter or value, for example an electrical current, and the actual value provided by the valve, for example a pressure.Therefore, the reference values which are stored in the programmers can only be converted into defective actual values, and this has a disadvantageous influence on the quality of the plastics article produced.

Attempts have been made to adjust the valves with actuating means which can convert hydraulic or electrical signals into precise mechanical stroke movements (Austrian patent specifications Nos 336 878 and 336 877). However, these actuating means cannot compensate for non-linearities which are caused by the valve itself.

Regulating systems have also already been developed, which are intended to permit coincidence as between the reference value and the actual value, by continuously measuring the actual value and suitably re-adjusting the valve.

However, regulating systems of this kind are technically complicated and expensive and tend to suffer from instability.

For example British patent specification No 1 486 883 discloses a control means for an injection moulding machine, which compares the reference values to the actual values by means of a comparator. The comparator checks whether the actual value is within a given range of tolerances, and can form four different defect signals, in dependence thereon. In this connection, the comparator provides an indication as to whether the actual value is within the tolerance range and whether it is greater or smaller than the reference value. In dependence on the respective defect signal, a given position in a correction memory is called up after each operating cycle, in which position a correction instruction for removing the corresponding defect is stored.

A disadvantage of this control means is that it is machine-bound, that is to say, it can only be used for a particular given machine, as the correction instructions associated with the defect signals can in fact only be used for a given machine. Accordingly, a very high level of expenditure in regard to programming is required for the correction memory as for example an injection moulding machine has a plurality of adjusting members and therefore a very large number of combinations of defects are also possible.

The invention is accordingly based on the problem of providing a control means for adjusting members in plastics processing machines, in which inaccuracies in respect of the adjusting members or non-linearities as between the adjusting parameters and the actual values are compensated.

According to the invention, for this purpose there is provided a randomly triggerable checking value programmer for issuing a series of checking values which are distributed over the adjustment range of the adjusting member, wherein the evaluation circuit forms correction values corresponding to the checking value-actual value differences, and stores them in a correction value memory, and that the adjusting parameters initiated by the reference value programmer are corrected in accordance with the associated correction values.

The invention thus departs from regulation-like systems in that it avoids adjusting members being continuously actuated with adjusting values which do not correspond to their adjusting value-actual value proportion. The checking value programmer provided for this purpose virtually performs a calibration operation before the machine is put into operation, with the evaluation circuit forming correction values in dependence on the differences between the checking values and the actual values. The reference values which are contained in the reference value programmer can then be amended from the outset by the appropriate correction values which contain precise information about the respective reference value-actual value differences.

With the present invention, it is therefore in principle not necessary for the actual position of the adjusting members to be monitored during operation. During operation, renewed triggering of the checking means is generally not necessary as the relationship between the adjusting value and the actual value of the adjusting member generally remains constant over a prolonged period of time.

In contrast, in the event of a change of adjusting member or when a repair is made, the checking means can be triggered again so that the reference values of the programmer can be adapted to the new conditions.

An embodiment of the invention is described hereinafter with reference to the accompanying drawings wherein:~ Figure 1 shows a diagrammatic view of an injection moulding machine, Figure 2 shows the relationship between adjustment value and actual value of an adjusting member, and Figure 3 shows a block circuit diagram of the control means according to the invention.

Figure 1 indicates the injection moulding mould 6 and the injection unit of a screw injection moulding machine. The latter has a screw 5 which is disposed within an injection and plasticising cylinder and which is rotatable by means of a hydraulic motor 7 and slidable by means of a hydraulic piston-cylinder unit 8. The hydraulic piston-cylinder unit 8 is connected to a pump 4 by way of a hydraulic line 3, with two adjusting members 1 and 2 being disposed in the hydraulic line 3. The adjusting member 1 is a pressureproportional valve and the adjusting member 2 is a quantity-proportional valve. The pressure applied to the screw 5 can thus be adjusted by suitable actuation of the adjusting member 1, while the adjusting member 2 is operable to control the feed speed of the screw 5.The actual value in respect of speed is measured by means of an inductive generator or sensor 9 and the actual value in respect of pressure is measured with a generator or sensor 10. Now, during the injection ope#ration, a first programmer 15' issues distancedependent speed reference values, according to the respective requirements. The speed reference values control the adjusting member 2 by way of a checking means 1 6. After the injection operation is concluded, a second programmer 15 issues time-dependent pressure reference values to the adjusting member 1.

It will be appreciated that the invention can be applied not just to the two above-mentioned adjusting members, and likewise the number of reference values which are issued to the adjusting member during a working operation is not an essential factor.

Figure 2 now shows the relationship between the adjusting value and the actual value of a pressure proportional valve. The broken line A in Figure 2 represents the ideal, strictly linearly proportional relationship between the adjusting value and the actual value. In actual fact however, due to various tolerances and limiting conditions, the relationship is for example that shown by the line B. The reference values which are introduced into the programmer 15, on the assumption of linear proportionality, are therefore only converted into defective actual values.

Now, according to the invention, the checking means 16 shown in Figure 3 is provided to eliminate such errors. The checking means 16 is connected by way of a first digital-analog converter 18 to a pressure actual value generator or sensor 10 and by way of a second digitalanalog converter 18 and amplifier 19, to the pressure proportional valve 1. For the purposes of triggering the checking means 16. there is a checking button 17 which sets a time control means 20 in operation. Now, in accordance with a first eiTibdimerlt, the time control~ means 20 successively calls up a succession of checking values P , P, P, from a checking memory 22, and thus actuates the pressure proportional valve 1, by way of the digital-analog converter 18 and the amplifier 19.The checking reference values cover the adjustment range of the pressure proportional valve 1 for example in linear 4% steps.

The respective actual values are communicated to the checking means 16 by the pressure actual value generator 10, by way of the digital-analog converter 18. An evaluation circuit 21 now compares each checking value P, to Pn to its actual value and stores the difference between the two values, as a correction value K1, K2 Knl in a correction memory 23.

During operation, each reference value P1 (t), P2(t)... Pn (t) of the programmer 15 can be modified by the difference Kt, K2 to Kn which is associated with the identical checking value P, P2 to Pn It is also possible however for the modification or correction of the reference values of the programmer 15 to be performed at the same time as or subsequent to determination of the correction values K, to Knl and for the corresponding corrected reference values of the programmer 15 to be stored.

As shown in Figure 2, for a checking reference value of 20 bar, there would be for example an actual value of 14 bar and accordingly a correction value of for example + 6 bar. Therefore, a program reference value of 20 bar would be converted into a corrected reference value of 26 bar, in which respect it will be seen from the Table that this now results in the desired actual value of 20 bar.

In a second embodiment of the invention, the checking means 16 again presets checking values covering the adjustment range of the adjusting member. The evaluation circuit 21 now determines a succession of actual values and stores them with the associated checking values, as correction values. Each reference value of the programmer 15 can now be converted by comparison with the actual values, into a checking value which is associated with the identical actual value, as the adjusting parameter. For example, the evaluation circuit again determines a linear succession of actual values in 4% steps.

The invention therefore makes it possible also to use adjusting members which hitherto had to be replaced due to lack of linearity. The invention is also not restricted to the two embodiments described above for determining correction values in respect of the reference values of the programmer. Particularly when an adjusting member has a severely fluctuating linearity defect, it is advantageous for the tendency of the linearity defect to be taken into account when determining the correction values, in accordance with the first embodiment. It is also possible to indicate excessive deviations as between checking reference values and actual values, in the form of an alarm signal, if the function of the adjusting member seems to be detrimentally affected thereby.

Claims

1. A control means for adjusting members which are operable in a multi-stage or continuous manner, in plastics processing machines, in particular for electromagnetic proportional valves in injection moulding machines, having at least one reference value programmer for issuing reterence values to an adjusting member, an actual value generator and an evaluation circuit which corrects the corresponding parameters for the adjusting member in dependence on the reference value-actual value differences, wherein there is provided a randomly triggerable checking value programmer for issuing a series of checking values (Pr, P2... Pn) which are distributed over the adjustment range of the adjusting member, wherein the evaluation circuit forms correction values (K1, K2... Kn) corresponding to the checking value-actual value differences, and stores them in a correction value memory, and the adjusting parameters initiated by the reference value programmer are corrected in accordance with the associated correction values (K1, K2...

2. A control means according to claim 1 wherein the checking value programmer has a time control means and a checking value memory from which a succession of checking values (P1, P2... Pn) can be successively called up, wherein the evaluation circuit compares each checking value (P1, P2... Pn) to its actual value and stores the difference as a correction value (K1, K2... Kn) in the correction value memory, and each reference value (Pr (t), P2(fl... Pn (t) of the reference value programmer is corrected by the correction value (K1, K2... Kn) associated with the identical checking value (P1, P2...

3. A control means according to claim 1 wherein the checking value programmer has a time control means and a checking value memory from which a succession of checking values (P1, P2... Pn) can be successively called up, wherein the evaluation circuit stores the associated actual values as correction values (K1, K2.. . Kn) and each reference value (Pss (t), P2(t)... Pn (t)) of the reference value programmer is converted into a checking value (P1, P2.. P,) which is associated with the identical actual value.

4. A control means for adjusting members which are operable in a multi-stage or continuous manner, in plastics processing machines constructed and arranged substantially as hereinbefore described and shown in the accompanying drawings.