Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~CK~ROI]ND OF T~lr INVt.NT-.LON
- FIELD OF THE INVENTION
The invention relates to a device on a toggle lever
injection moulding machine with two mould carrier
plates being movable relative to each other, one
mould carrier plate being movably mounted on traverses
and linked to a hinge plate by means of a toggle
lever mechanism, said device comprising a motor
or the like for adjusting the position of said
hinge plate in the longitudinal direction of said
traverses in order,to set the mould locking force,
and measuring means determining the mould locking
force.
DESCRIPTION OF THE PRIOR ART
With toggle lever injection moulding machines the
mould locking force is set by changing the die space
by moving the hinge plate until the toggle lever can
still just be moved into its final positlon. This
setting requires great experience of the operating 'I
staff and a subjective decision as to when this ',
position has been reached.
It is a further disadvantage of toggle lever
injection moulding machines that the die space is
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changed because of changes in temperature, which
also affects the mould locking force. When the die
space is increased due to an increase in temperature,
the locking force of the machine is increased as
S well, whereas the locking force is reduced in the
case of a decrease of temperature.
Mechanical gauges or the like have been disposed
on toggle lever injection moulding machines, which
register the stretch of the traverses when the
mould is closed, so that the mould locking force
can also be indicated. As the stretch of the traverses
amounts only to some hundreths of a millimeter very
little importance has been att,ached to these measuring
results.
Automatic setting of the mould locking force has been
tried. A dynamometer was disposed in the feeding line
or directly on the driving means for the toggle lever
system. In this device means for controllin~ the
displacement path of the movably mounted carrier plate
are provided, which a low theanalyzing of the measured
value of the dynamometer only within certain
displacement ranges. This way of setting the mould
locking force has the disadvantage, that the required
machines and operations are very complicated and,
moreover, that the results are relatively inaccurate.
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This is due to the fact, that the considerable
friction losses in the toggle joints cannot be taken
into consideration, and that consequently the force
for driving the toggle joint system is not directly
proportional to the mould locking force.
SUMMARY OF THE INVENTION
It is, therefore, the object of the present invention
to provide a device on a toggle lever injection
moulding machine of the above-mentioned kind
allowing an exact setting and levelling of the mould
locking force.
According to the invention this is achieved by adapting
the measuring means to serve in known manner as
tensometer for a traversel a processingdevice being
connected with said tensometer and controlling said
- 15 motor.
By simple constructional means the mould locking force
can, thus, be kept constant, even in the case of long
operation resp. changes in temperature. This is
particularly surprising in view of the very low
longitudinal stretch of the traverse during the
closing movement.
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Friction losses in the driving means of the toggle
lever system and in the toggLe lever ~oints do not
vitiate the measuring results.
An embodiment of the present invention is characterized
in that the processingdevice has an input amplifier
connected with said tensometer, a difference amplifier
determining the variance of the set and actual value,
the output of said difference 3mplifier being connected
with a first and second comparator fixing the tolerance
~0 limits, said first and said second comparator being
linked with memories, an adjustable master clock
being provided to read out the content of said
memories and to actuate said mQtor.
BRIEF DESC~IPTION OF THE DRAWINGS
,
In the following an embodiment of the invention will
be described in more detail without being limited
thereto.
Figure 1 shows the construction scheme of a toggle lever
injection moulding machine and
Figure 2 shows the basic circuit diagram of a processing
device in accordance with the present invention.
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DESC~IPTION OE` THI~ YE~R~D ~:MBOVl~l~`NT
As can be seen in fig. 1, one mould half 3' is
mounted on a mould carrier plate 2' provided with
four traverses 1. A further mould carrier plate 2
is movably mounted alongside said traverses 1,
said mould carrier plate 2 carrying the second
mould half 3. The mould carrier plate 2 and the
mould are linked to a hinge plate by means of a
toggle lever mechanism 4, the position of said
hinge plate being variable in the longitudinal
direction of the traverses by means of an adjusting
device 5.
The mould locking force can, therefore, be set by
means of the adjusting device--5. For this purpose said
ad~usting device 5 is connected with a motor 6 by
means of a cogged wheel. Moreover, a tensometer 7,
e D g. an inductive displacement transducer, is disposed
on one traverse 1, said tensometer emitting a signal
porportional to the effective mould locking force.
This actual value signal is fed to a processing device 8.
The plotting device 8 has two outputs actuatlng the
motor 6. Furthermore, the plotting device 8 comprises
a setting element 9 for the set value, an indicator 10
for the mould locking force and setting means 11 for
the tolerated deviation of the mould locking force from
the set value. The structure of theprocessing device
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corresponds to the principle indicated in fig. 2.
The actual value of the tensometer 7 is fed to a
difference amplifier 13 by means of an input
amplifier 12, the second input of said difference
amplifier 13 being connected with the setting means 9
for the set value. The difference amplifier 13,
therefore, emits an output signal proportional to
the variance of the mould locking force and the
set value. This output signal is fed to two comparators
16 and 17. The comparator 16 is connected with the
setting means 14 for the upper tolerance limit of the
locking force, whereas the comparator 17 is connected
with the setting means 15 for the lower tolerance
limit. When the pre-determined_tolerance limit is
exceeded, one of the two comparators 16 and 17 emits
an output signal which can be read into the memory 18.
The read-in-order is given by the transfer line 19,
when the closing process has been finished. When
exceeding resp~ falling below the pre-determined
range of tolerance, a correcting signal is obtained
at the output of the respective memory 18. Said signal
is read out after the opening process by means of the
- corresponding AND-operators 23. The duration of the
setting impulse can be chosen by means of an adjustable
master clock 21. Said duration is independent of the
amount of the deviation of the locking force.
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C`onsequently, the machine requires a longer setting
period at the start, but an excessive and critical
change of the locking force is avoided.
After terminating the setting impulses the
memories 18 are cleared by the reset element 22.
The AND-operators 23 are provided with suitable
drivers 24, e.g. a relay.
A machine of the above-described kind can automatically,
step by step,reach the pre-determined mould locking
force. In order to make an exact measuring of the
locking force possible, it is of advantage to
associate a correcting element with the difference
amplifier 13 in order to obtain the setting of the
zero point.
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