Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1171757
The present invention relates to a control
device for the hydraulic circulation in a plastics material
injec~ion moulding machine, with the delivery output of the
variable delivery pump being adapted to the various require-
ments 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
adjusta~le by means of electrical input signals, whereby
a return con~rol 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 ~ Patent 1,548,016~,
the proportional valve system includes both a proportional
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 deyice produces a geo-
metrical parameter, in that the position of the valve body o~
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 ou~put requirements of the consumer apparatus at a
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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 pro-
vided 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 cross-section of such a valve system
being ad~ustable 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
read~usts the variable deliyery pump, and whereby the propor-
tlonal valve system is provided in the regulating circuit with
at least one position transducer by means of which transducer
and ad~ustment 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 valye system is
automatically convertible to a pressure program regulation by
means of a pressure gauge in accordance with at least one
para~eter (path, time, pressure) for specific pressure require-
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1~71757
ments (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 i8 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, howeyer, as the basis for the opera-
tion and the control of the deliyery 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 yalve 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. How~
ever, 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,
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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 construct;on; 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 provlded with drive motor 17 of pump section 11, to
the oil ~ilter 18. A llne 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
piStOIl pump9 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.
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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 ~ain supply line
13 which leads from the variable delivery pump 16 to the con
sumer apparatus and has a portion 13a, located upstream of
the proportional quantity flow control valve 12, and a portion
13b, located downstream of this val~e. The feedbac~ line 22
branches off from the main supply line 13 in the portion
13_, 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
15 i5 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 12d at the pre-control or
preliminary stage 12b of the flow control valve 12 co-operates
with a directionai scanner or position transducer 12c. l'he
position transducer 12c 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 12b 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 appropria~e adjustment
of the valve body of the proportional response flow control
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valve 12 by means of the position transducer 12c via the pre-
control stage 12b , the pressure in the feedback line 22 may
be reduced at that particular location in the portion 13b of
the main supply line 13 where the pressure gauge 24 reduces
the pressure during pressure programme control.
The section 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 ~rogram, constitutes the basis for the present control .
device, ~n 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 trans-
ducer 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 13b
downstrea~ 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 13b downstream of the flow
control valve 12. The pressure difference may be, for examp7e,
11 bars. This parameter denotes alower limit at which the
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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 accor-
ding to program 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
crlterion if a specific signal ~ariable, which i8 predetermined
in the computer, is exceeded. According to the pressure
progra~, 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 o~ the in-
~ection moulding die in the tool securing phase. In turn~ this
pressure program control can be switched-oyer to a quantity
program control, disposed di~ectly on the consumer apparatus,
according to a variable which is predetPrmined 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
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control is a combined quantity and pressure program control
whereby the proportional quantity valve is no longer directly
controlled by the position transducer 12_, but, for example,
by the section voltage transformer 26 or by the pressure gauge
24. In each case, however, such a subsequent readiustment of
the pump 16 is ensured by means of the feedback line 22 that
the pressure drop between the pump 16 and the portion 13b of
the consumer line is a constant, minimal size.
In the embodiment shown in the drawing, the
pressure gaùge 24, as stated above (page 5), reduces the pres-
sure 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
confiumer appara~us 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 con-
trolling the pressure in the moulding cavity. It cannot,
therefore, replace the pressure gauge 24, which is responsible
for the o~her remaining ranges of pressure control where, for
example, the operation must be carried out at maximum pressure
or vhere the injection moulding die is closed at low pressure.
The further pressure gauge may be supported by
a s~rew-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.
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1171757
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 super-
poses the conventional pressure regulation by means of pressure
gauge 24.
A working cycle, which is regulated by the con-
trol device, operates in the following steps, e.g. starting
from the opened injection moulding die:
1. The injection mouldlng die is closed. The closure move-
ment required therefor may be executed at different speeds. The
quantity program necessary therefor is regulated by the position
transducer 12c or the section voltage transformer 26. During
the clcsing movement, ~ safety path for the injection moulding
die is travelled-over, in which a pressure regulation is super-
posed over the speed regulation via the pressure gauge 24.
This means that, when the permissable 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 12c 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
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is regulated via the position transducer 12c 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 sub-
sequent pressure program. This occurs via a pressure gauge
ln 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 ~orm is effected via a hydraulic motor.
The quantity program regulation which is required therefore
occurs yia the directional scanner 12c or via the section
voltage transformer 26.
5. Subsequently, the injection nozzle is detached from the
injection moulding die via a speed program (quantity progrem).
6. The injection moulding die is then opened. The opening
moyement required therefor may be executed at different speeds.
The quantity program required therefor is regulated via the
posi-tion transducer 12c or via the section voltage transformer
26.
7. The finlshed moulding is ejected. During forward movement
and during backward moyement, the hydraulic ejector is controlled
by a speed program haying a superimposed printed program. The
regulation is thereby effected via the position transducer 12c
or via the section voltage transformer 26 and the pressure
gauge 24.
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