GB2099610A

GB2099610A - A control device for the hydraulic circuit of an injection moulding machine

Info

Publication number: GB2099610A
Application number: GB8209559A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-05-14
Filing date: 1982-03-31
Publication date: 1982-12-08
Also published as: IT1200573B; FR2506041A1; NL8200963A; ATA157682A; CH659427A5; JPS57195633A; CA1171757A; FR2506041B1; DE3119095C2; IT8220316A0; GB2099610B; DE3119095A1; AT376170B

Abstract

In a plastics material injection moulding machine a control device for the hydraulic circuit including a variable delivery pump 16 controlled by means of a proportional valve system 12 wherein the throughflow cross-section of said valve system is adjustable by means of electrical input signals, whereby a feedback line 22 is provided for readjustment of the variable delivery pump, and whereby the proportional valve system has a regulating circuit 12d which is provided with at least one position transducer 12c by means of which an adjustment of the proportional valve system is effected characterised in that quantity program regulation of the proportional valve system is automatically convertible to a pressure program regulation by means of a pressure gauge 24 in accordance with at least one parameter (path, time, pressure) for specific pressure requirements, the pressure gauge 24 being locatable in the regulating circuit of the proportional valve system instead of the position transducer 12c during the pressure program regulation; and in that the delivery pump 16 is controllable by means of the feedback line 22 in dependence upon the pressure prevailing in a portion 13b of the main supply 13, the control being such that there is a constant drop in the operating pressure between the delivery pump 16 and the said portion 13b of the main supply line. <IMAGE>

Description

SPECIFICATION A control device for the hydraulic circuit of an injection moulding machine The present invention relates to a control device for the hydraulic circulation in a plastics material injection moulding machine, with the delivery output of the variable delivery pump being adapted to the various requirements of the consumer apparatus during the working phases of a working cycle by means of a proportional valve system, the throughflow cross-section of such a valve system being adjustable by means of electrical input signals, whereby a return control or feedback line is provided which branches-off from the consumer or main supply line downstream of the proportional valve system and readjusts the delivery pump, and whereby the proportional valve system is provided in the regulating circuit with at least one position transducer, by means of which transducer an adjustment of the proportional valve system deviating from the desired value is effected to return to the predetermined desired value of the program.

In a known control device of this type (German Offenlegungsschrift 2 528 963 or equivalent GB Patent 1 548 016), the proportional valve system includes both a propotional quantity valve and a proportional pressure valve, and a position transducer is located in the regulating circuit of each of these valves. Such a control device produces a geometrical parameter, in that the position of the valve body of each proportional valve can be regulated. This results in a qualitatively precise control for the ranges, especially pressures and speeds for the consumer apparatus, whereby the energy consumption by the delivery pump is adapted to the actual output requirements of the consumer apparatus at a lower limit.

Based on this, the invention seeks to modify a control device of the above-mentioned type in such a manner that it can satisfy the most varied program conditions to a substantially higher degree, especially also with regard to a pressure program control device which is located directly on the consumer apparatus, and in such a manner that, in this case, the regulating pump is operated so as to adapt to a minimal, energy requirement.

According to the present invention there is provided a control device for the hydraulic circuit of a plastics material injection moulding machine, with the delivery quantity-pressure output of the variable delivery pump being adapted to the various requirements of the load during the working phases of a working cycle by means of a proportional valve system, the throughflow crosssection of such a valve system being adjustable by means of electrical input signals, whereby a feedback line is provided which branches-off from the main supply line downstream of the proportional valve system and readjusts the variable delivery pump, and whereby the proportional valve system is provided in the regulating circuit with at least one position transducer by means of which transducer an adjustment of the proportional valve system deviating from the desired value is returnable to the predetermined desired value set by the program, characterised in that the quantity program regulation of the proportional valve system is automatically convertible to a pressure program regulation by means of a pressure gauge in accordance with at least one parameter (path, time, pressure) for specific pressure requirements (e.g. subsequent pressure phase during injection or tool-securing phases in die-closure), the pressure gauge being located in the regulating circuit of the proportional valve system instead of the position transducer during the pressure program regulation; and in that the delivery pump, during quantity program regulation and during pressure program regulation, is controllable by means of the feedback line in dependence upon the pressure prevailing in a portion of the main supply downstream of the proportional valve system, the control being such that, during quantity program regulation and during pressure program regulation, there is a constant drop in operating pressure between the delivery pump and the said portion of the main supply line.

What is understood by a "drop in operating pressure" (operational pressure gradient) in the above sense is such a drop which is required, however, as the basis for the operation and the control of the delivery pump and lies at this lower limit.

In such an embodiment, the regulation may also be effected in direct dependence upon the pressure of the hydraulic medium. In fact, the position of the valve body in the proportional valve system is also regulated in this case by means of a directional scanner or position transducer, which co-operates with the control magnet, to a program-controlled cross-sectional change which is repeated in the cycle. However, the output requirement of the delivery pump is now determined in dependence upon the development of pressure in the consumer line downstream of the proportional quantity valve, the feed pump having a constant, minimal feed pressure, and this is a pre-requisite for maximum energy-saving.

The control system according to the invention also has the structural features required for a relatively simple, and hence economical construction; because such a system can be operated with one single proportional quantity valve at high speed.

In addition to the pressure gauge, a path or section voltage transformer may be located in the regulating circuit of the proportional valve system for various speed stages and is disposed directly on the consumer apparatus.

The invention will be described further, by way of example, with reference to the accompanying drawing, which is a diagrammatic view of the hydraulic circuit of the control device.

A control device is illustrated including a valve group 10, a pump group 11 and a group 50 having a section voltage transformer 26 for speed regulation with regard to very different speed stages-this being synonymous with a quantity program regulation.

A line 25 leads from variable delivery pump 16, which is provided with drive motor 17 of pump section 11, to the oil filter 18. A line 30 leads from the oil filter 18 to fluid reservoir 19. A reservoir line 14 comes from the valve section 10 and discharges into the reservoir 19. The variable delivery pump which may, for example, be a radial piston pump, an axial piston pump or a radial vane type pump, is provided with a control member 20.

A feedback line 22, which comes from the valve section 10, leads to the control member 20.

The valve section 10 includes a proportional quantity control valve 12 which has a high working rate and a valve portion 12a located in the consumer or main supply line 13 which leads from the variable delivery pump 16 to the consumer apparatus and has a portion 13a, located upstream of the proportional quantity flow control valve 12, and a portion 13b, located downstream of this valve. The feedback line 22 branches off from the main supply line 13 in the portion 136, i.e. downstream of the control valve 12, in order to control the pump 16 in dependence upon the pressure in the main supply line 13.

A constrictor member 21 (attenuation diaphragm) is arranged in the feedback line 22. A pressure relief valve 1 5 is located in a bridging or connecting line 23 between the portion 13a of the main supply line 13 and the reservoir line 14.

The control electromagnet 1 2d at the pre-control or preliminary stage 1 2b of the flow control valve 12 co-operates with a directional scanner or position transducer 12c. The position transducer 1 2c is therefore located in a regulating circuit, by means of which circuit values of the proportional response flow control valve, which deviate from the desired value, are returned to the desired value. The preliminary control stage 1 2b may be supplied alternately by an external control oil source 27 via line 29 or by an internal control oil source which is formed by a tapping line 28 which extends from the main supply line 13 in the portion 13a.

During control of variable speed stages according to the predetermined program based on an appropriate adjustment of the valve body of the proportional response flow control valve 12 by means of the position transducer 1 2c via the pre-control stage 1 2b, the pressure in the feedback line 22 may be reduced at that particular location in the portion 1 3b of the main supply line 13 where the pressure gauge 24 reduces the pressure during pressure programme control.

The second voltage transformer 26 in the section 50 for regulating various speed stages, i.e.

for quantity regulation, has a voltage portion U.

A linear potentiometer or a rotary potentiometer may be used, for example, as a voltage transformer.

The control device may be used in numerous ways: The adjustment or setting of the control valve 12, which is predetermined in a computer, i.e.

operates according to program, constitutes the basis for the present control device, in that a quantity or pressure setting of the control valve 12, deviating from the desired value is returnable to the desired value alternately by means of the position transducer 12c, the section voltage transformer 26 or the pressure gauge 24 in the regulating circuit. The output requirements, which change continuously thereby during the working cycle of the consumer apparatus, e.g. speeds and pressures, are taken into consideration by an appropriate control of the regulating pump via the feedback line 22 in dependence upon the pressure of the main supply line 13 in the portion 1 3b downstream of the control valve 12.The pressure gradient between the pump 16 and the main supply line 13 is always kept constant thereby in the portion 1 3b downstream of the flow control valve 12. The pressure difference may be for example, 11 bars. This parameter denotes a lower limit at which the pump is still operational and controllable. The basis for the control is, therefore, a quantity control which, by means of the position transducer 12c, is a geometrical parameter, namely the setting of the valve body of the proportional quantity flow control valve, such adjustment occurring according to programe in the injection cycle. This quantity control is superposed by a pressure program control. Depending on the requirements of the consumer apparatus, the control device is automatically switched-over from the quantity control to the pressure program control.The switch-over Is effected according to predetermined criteria, e.g. according to the path covered at the consumer apparatus, or in dependence upon the time or by means of the pressure gauge 24 in dependence upon the oil pressure in the consumer line or upon a pressure gauge disposed directly on the consumer apparatus. The transition from the quantity program control to the pressure program control is effected within the range of every single criterion if a specific signal variable, which is predetermined in the computer, is exceeded.

According to the pressure program, control is effected, for example, in the subsequent pressure phase after the plastics material has been injected into the injection moulding die and during closure of the injection moulding die in the tool securing phase. In turn, this pressure program control can be switched-over to a quantity program control, disposed directly on the consumer apparatus, according to a variable which is predetermined in the computer, and the quantity program control operates on the basis of the group 50 having a section voltage transformer for speed regulation. Accordingly, the so-called pressure program control is a combined quantity and pressure program control whereby the proportional quantity valve is no longer directly controlled by the position transducer 1 2c, but, for example, by the section voltage transformer 26 or by the pressure gauge 24.In each case, however, such a subsequent readjustment of the pump 16 is ensured by means of the feedback line 22 that the pressure drop between the pump 16 and the portion 1 3b of the consumer line is a constant, minimal size.

In the embodiment shown in the drawing, the pressure gauge 24, as stated above (page 5), reduces the pressure at that location of the consumer line 13 at which the pressure in the feedback line 22 is reduced However, the pressure gauge 24 may also be disposed directly on the consumer apparatus in the consumer line 13.

In many cases, it may be expedient to provide a further pressure gauge in addition to the pressure gauge 24~this further pressure gauge reducing the pressure in the moulding cavity of the injection moulding die. This further pressure gauge is intended for this purpose and, in connection with the scope of pressure regulation.

is suitable for controlling the pressure in the moulding cavity. It cannot, therefore, replace the pressure gauge 24, which is responsible for the other remaining ranges of pressure control where, for example, the operation must be carried out at maximum pressure or where the injection moulding die is closed at low pressure.

The further pressure gauge may be supported by a screw-bolt which extends through the wall of the injection moulding die. Consequently, it is capable of being easily removed from this injection moulding die and being reinsertable.

However, the further pressure gauge may also be disposed on the rear side of an ejector pin of the injection moulding die, because this ejector pin defines the moulding cavity with its front leading edge and is, therefore, suitable for transmitting the pressure data of the moulding cavity to the pressure gauge disposed on the rear side.

The further pressure gauge is, therefore, an important component part of a regulating facility which superposes the conventional pressure regulation by means of pressure gauge 24.

A working cycle, which is regulated by the control device, operates in the following steps, e.g. starting from the opened injection moulding die: 1. The injection moulding die is closed. The closure movement required therefor may be executed at different speeds. The quantity program necessary therefor is regulated by the position transducer 1 2c or the section voltage transformer 26. During the closing movement, a safety path for the injection moulding die travelled-over, in which a pressure regulation is superposed over the speed regulation via the pressure gauge 24. This means that, when the permissible pressure is reached which is envisaged by the program, pressure regulation occurs automatically.

2. The injection nozzle is brought to the injection moulding die-this happens via a speed program with a superposed pressure program.

The regulation-is thereby effected via the position transducer 1 2c or via the pressure gauge 24.

3. The plastics material is injected into the injection moulding die. Injection is effected via a speed program which is synonymous with a quantity program. This quantity program is regulated via the position transducer 1 2c or the section voltage transformer 26. The quantity program is superposed by a pressure safety means via the pressure gauge 24. After a pressure, envisaged by the program, has been reached in the injection moulding die, there is a switch-over to a subsequent pressure program.

This occurs via a pressure gauge in the injection moulding die or a pressure gauge in the hydraulics, i.e. preferably in the control valve 12 or on the injection cylinder.

4. The plastics material is plasticised, by means of the plasticising worm, into plasticising cylinders (injection cylinders) via a speed program. In this case, the drive of the plasticising worm is effected via a hydraulic motor. The quantity program regulation which is required therefor occurs via the directional scanner 1 2c or via the section voltage transformer 26.

5. Subsequently, the injection nozzle is detached from the injection moulding die via a speed program (quantity program).

6. The injection moulding die is then opened.

The opening movement required therefor may be executed at different speeds. The quantity program required therefor is regulated via the position transducer 1 2c or via the section voltage transformer 26.

7. The finished moulding is ejected. During forward movement and during backward movement, the hydraulic ejector is controlled by a speed program having a superimposed printed program. The regulation is thereby effected via the position transducer 1 2c or via the section voltage transformer 26 and the pressure gauge 24.

Claims

1. A control device for the hydraulic circuit of a plastics material injection moulding machine said device including a variable delivery pump having a delivery quantity-pressure output through a main supply line adaptable to the various requirements of the load during the working phases of the working cycle of the machine by means of a proportional valve system wherein the throughflow cross-section of said valve system is adjustable by means of electrical input signals, whereby a feedback line is provided which branches-off from the main supply line downstream of the proportional valve system for readjustment of the variable delivery pump, and whereby the proportional valve system has a regulating circuit which is provided with at least one position transducer by means of which transducer an;;adjustment of the proportional valve system deviating from the desired value is effected to return to the predetermined desired value set by the program, characterised in that the quantity program regulation of the proportional valve system is automatically convertible to a pressure program regulation by means of a pressure gauge in accordance with at least one parameter (path, time, pressure) for specific pressure requirements, the pressure gauge being locatable in the regulating circuit of the proportional valve system instead of the position transducer during the pressure program regulation; and in that the delivery pump, during quantity program regulation and during pressure program regulation, is controllable by means of the feedback line in dependence upon the pressure prevailing in a portion of the main supply downstream of the proportional valve system, the control being such that, during quantity program regulation and during pressure program regulation, there is a constant drop in operating pressure between the delivery pump and the said portion of the main supply line.

2. A device as claimed in claim 1, in which the proportional valve system is formed by a single proportional quantity valve having a high operating speed.

3. A device as claimed in claim 1 or 2 in which in addition to the pressure gauge, there is a voltage transformer located in the regulating circuit of the proportional valve system for various speed stages, and said transformer is mounted directly on the consumer portion of the machine.

4. A device as claimed in any of claims 1 to 3, in which the position transducer or a voltage transfotmer can be alternately connected into the regulating circuit of the proportional valve system for the' quantity program regulation which serves to achieve various speed rates in the consumer portion of the machine.

5. A device as claimed in any of claims 1 to 4, in which the signal variables, which are required within each parameter and trigger the changeover from the quantity program regulation to pressure program regulation, are predetermined for a specific working cycle in the computer.

6. A device as claimed in any of claims 1 to 5, wherein a constrictor member is inserted in the feedback line.

7. A device as claimed in any of claims 1 to 6, wherein the constant pressure difference between the regulating pump and the said portion of the consumer line is between 8-14 bars.

8. A device as claimed in any of claims 1 to 7, wherein the proportional valve system is selectively fed by an internal control oil source or an external control oil source.

9. A device as claimed in any of claims 1 to 8, in which the pressure relief valve is introduced into the main supply line in a portion upstream of the proportional quantity valve.

10. A device as claimed in any of claims 1 to 9, in which the pressure in the control feedback line is reduced during the quantity program regulation and the pressure in the pressure gauge is reduced during the pressure program regulation at the same location in the main supply line.

11. A device as claimed in any of claims 1 to 10, in which the pressure gauge is disposed directly on the consumer apparatus in the main supply line.

12. A device as claimed in any of claims 1 to 9, in which in addition to the pressure gauge, a further pressure gauge is provided which reduces the pressure in the moulding cavity of the injection moulding die.

13. A device as claimed in claim 12, in which further pressure gauge is supported by a screwbolt which extends through the wall of the injection moulding die.

14. A device as claimed in claim 12, in which further pressure gauge is disposed on an ejector pin of the injection moulding die.

15. A control device constructed and arranged to operate substantially as herein described with reference to the accompanying drawings.