Drive control apparatus for an injection-molding machine

A control arrangement for moving tools brings these tools quickly into a desired position smoothly and without shock. The arrangement comprises means for preadjusting the required displacement so that the whole displacement path corresponding to the movement sweep of the tool is first determined. A calculation member (4) converts a given delay of the tool movement into a value corresponding to the speed of movement. An integrator (6) derives from the calculated speed value as a function of time a required position value. Upon movement of the tool the means for preadjusting the required displacement are continuously readjusted and the adjusted value for the drive (25) is determined by means of a comparison with the position value supplied by the actual displacement pick-up device (8).

This invention relates to a drive arrangement for controlling the movement 
of tools, notably of mould parts of a machine for injection-moulding of 
synthetic material with the use of an actual displacement pick-up device, 
by which the tool movement is determined in a displacement-dependent 
manner. 
DE-OS 2324839 discloses an arrangement for controlling a drive for the 
movement of tools, notably of mould parts of a machine for 
injection-moulding of synthetic material, which, when the mould is opened 
and closed, measures the actual speed of the movable mould parts and 
renders it equal to an adjustable nominal speed. When the mould is closed, 
the mould parts move at a constant speed towards each other until a given 
closing pressure is attained. The resulting collision of the mould parts 
leads to undesirable vibrations. These vibrations delay the closing 
process and increase the liability to wear. 
An object of the present invention is to provide an arrangement for 
controlling a drive by which tools, notably mould parts of a machine for 
injection-moulding of synthetic material, are quickly brought into the 
desired position, for example a closing position, such that they come to a 
standstill in the given final position smoothly and without shocks. 
According to the invention this object is achieved by a control arrangement 
comprising, means for preadjusting the required displacement, by which the 
whole displacement path corresponding to the movement sweep of the tool is 
first determined, a calculation member for converting a given delay of the 
tool movement into a value corresponding to the speed of movement, and an 
integrator which derives from the calculated speed value as a function of 
time a required position value, by which upon movement on the one hand the 
means for preadjusting the required displacement are continuously 
readjusted and on the other hand the regulated value for the drive is 
determined in comparison with the position value supplied by the actual 
displacement pick-up device. As a result, there is derived from a given 
displacement path corresponding to the movement sweep and from an 
adjustable delay a displacement-dependent speed profile which passes to 
zero towards the end of the movement sweep. 
According to an embodiment of the invention, the calculation member derives 
the speed of movement from the given delay of the tool movement, from the 
whole displacement path corresponding to the movement sweep and from the 
required position. The calculation member then derives at any instant the 
speed of movement, which the tool is not allowed to exceed, in order that 
the braking force to be transferred by the drive or by an associated 
braking device is sufficient to brake the tool until it comes to a 
standstill in its given final position. Since the delay can be chosen, the 
control arrangement can be used with differently dimensioned braking 
devices. 
An advantageous embodiment of the invention is characterized by a speed 
control circuit which is coupled between the calculation member and the 
integrator and comprises a series arrangement of a control amplifier 
driven by the calculation member and an integration member. The 
integration member supplies a nominal speed signal on the one hand via a 
feedback loop to the control amplifier and on the other hand to the 
integrator. The speed control circuit ensures that the tool is accelerated 
smoothly from its stationary position. 
A further embodiment of the invention is characterized by a speed limiter 
which is connected to the feedback loop and limits an acceleration signal 
supplied by the control amplifier to the integration member to a zero 
level when the nominal speed reaches a maximum speed predetermined by the 
speed limiter. In order to prevent complicated mould parts from being 
damaged when the injection mould is opened, it is advantageous to limit 
the speed of the movable mould parts. 
According to an embodiment of the invention, the speed limiter comprises an 
operational amplifier which compares the maximum speed with the nominal 
speed. The speed limiter according to the invention is of simple 
construction so that it can be manufactured at low cost and can operate in 
a reliable manner. 
An advantageous embodiment of the invention is characterized by at least 
one element for limiting the acceleration signal to a predetermined level 
and comprises a differential amplifier having an inverting input connected 
on the one hand via a feedback diode to the output of the differential 
amplifier and on the other hand to the input of the integration member. 
The non-inverting input of the differential amplifier receives a signal 
corresponding to the predetermined level of the acceleration signal. Due 
to the limitation of the acceleration, the energy consumption is reduced 
and the load of the--for example hydraulic--driving aggregate is 
diminished. 
In order that the invention may be readily carried out, it will now be 
described, by way of example, with reference to the accompanying drawing, 
in which:

The means for preadjusting the required displacement is constructed as an 
operational amplifier 1 which is supplied via the non-inverting input 2 
with the displacement path value corresponding to the whole movement sweep 
of the tool and via the inverting input 3 with the required position 
value. The means for pre-adjusting the required displacement control by 
means of the difference between the movement sweep (Z) and the required 
position value (W) is the calculation member 4, to which can be supplied 
via a control input 5 a value corresponding to the delay (B) of the tool 
movement. The calculation member 4 calculates therefrom the maximum speed 
of movement (V) which the tool is allowed to reach in order that it can be 
braked smoothly with a given delay until it comes to a standstill, with 
reference to the relation. 
##EQU1## 
The calculation member 4 can be followed by an integrator 6 which derives 
the required position from the speed of movement. The required position 
value is supplied to the non-inverting input of the comparator 7, which is 
constructed, for example, as an operational amplifier having an inverting 
input to which is supplied the position value of the tool determined by an 
actual displacement pick-up device 8. The difference between the required 
position and the position value is calculated by the comparator 7 and 
results in an adjusted value which can be supplied to the adjustment drive 
25 of a servo valve for the hydraulic drive of a movable injection-mould 
part. 
The calculation member 4 may also be followed by a control amplifier 9 and 
an integration member 10. The integration member 10 produces, from an 
acceleration signal formed by the control amplifier 9, a nominal speed 
signal which is supplied, on the one hand through a feedback loop 11 to 
the control amplifier 9, and on the other hand to the integrator 6 for 
producing the required position value. 
The signal supplied via the non-inverting input 2 to the operational 
amplifier 1 and corresponding to the whole movement sweep has the form of 
a positive step function. 
Since the required position of the tool is initially still zero at the 
beginning of a tool movement, the difference between the required position 
value and the movement sweep supplied by the amplifier 1 to the 
calculation ember 4, and the speed of movement derived by the calculation 
member 4, also have the form of a step function. Since the nominal speed 
signal fed back by the integration member 10 through the feedback loop 11 
to the inverting input 9a of the control amplifier 9 is initially zero, 
the acceleration signal derived by the control amplifier 9 from the 
difference between the nominal speed signal and the speed of movement 
signal assumes a high value. The integration member 10 produces therefrom 
the nominal speed value which starting from a zero value, increases 
steadily. The required position value produced by the integrator 6 then 
also steadily increases. 
The difference between the movement sweep and the required position value, 
which corresponds to the displacement path still to be covered by the 
tool, decreases so that the speed of movement derived by the calculation 
member 4 from this difference also decreases. The nominal speed increases 
when the speed of movement exceeds the nominal speed and therefore the 
acceleration signal produced by the control amplifier 9 is positive. Thus, 
the tool is accelerated. It is not until the speed of movement is lower 
than the nominal speed that the acceleration signal derived by the control 
amplifier 9 from the difference between the speed of movement and the 
nominal speed assumes a negative value and the tool is braked smoothly 
until it comes to a standstill in the final position. Since the braking 
operation immediately follows the acceleration process, the tool is moved 
in a very short time from the starting position to the final position. 
If the mould part is to be moved from the final position back to the 
starting position, a zero potential is applied to the non-inverting input 
2 of the operational amplifier 1. The required position has a positive 
value and is subtracted from this zero potential so that the difference 
between the movement sweep and the required position value, the speed of 
movement, the acceleration and the nominal speed have negative values. As 
a result, the required position value decreases and the tool moves 
smoothly back to the starting position. 
Differential amplifiers 12 and 13 limit the positive and negative 
acceleration signals, respectively. 
The inverting input of the differential amplifier 12 and of the 
differential amplifier 13 are electrically connected on the one hand to 
the connection lead between the control amplifier 9 and the integration 
member 10 and on the other hand each through a feedback diode 14 and 15, 
respectively, arranged in forward direction and in reverse direction, 
respectively, to the output of the differential amplifier 12 and 13, 
respectively. In the case of positive acceleration signals, the feedback 
diode 14 is conducting, while in the case of negative acceleration signals 
the feedback diode 15 is conducting. The inputs 12b and 13b, respectively, 
of the differential amplifiers 12 and 13, respectively, receive the 
positive and negative values, respectively, by which the positive 
acceleration signal and the negative acceleration signal, respectively, 
are limited. 
The nominal speed value signal is supplied to the inverting input 16a of a 
speed limiter constructed as an operational amplifier 16. The output of 
op-amp 16 is electrically connected through two switches 17 and 18 and 
four switching diodes 19 to 22 to the connection lead between the control 
amplifier 9 and the integration member 10. 
In the position shown in the Figure of the switch 23 a signal corresponding 
to the maximum speed of the tool from the starting position to the final 
position is supplied to the non-inverting input 16b of the operational 
amplifier 16. In the position shown in broken lines of the switch 23, a 
signal changed in polarity by the inverter 24 and hence corresponding to 
the maximum speed in the opposite direction is supplied to this input. 
In the direction of movement of the tool from the starting position to the 
final position, the switches 17, 18 and 23 have the position shown in the 
Figure. As long as the maximum speed is higher than the nominal speed, the 
operational amplifier 16 controls the switching diode 19 via the switch 17 
with a positive voltage so that the switching diode 19 is cut off and 
hence the acceleration signal can be limited only by the elements 12 to 15 
for limiting the acceleration signal. 
When the nominal speed reaches the value of the maximum speed, the output 
voltage of the operational amplifier 16 becomes zero and the switching 
diode 19 is switched to the conductive state. Via the switching diode 20 
and the switch 18, the input of the integration member 10 is then also 
coupled to the zero potential so that the nominal speed retains the value 
attained. 
It is not until the signal supplied by the calculation member 4 to the 
input 9b of the control amplifier 9 falls below the value of the nominal 
speed signal that the integration member 10 is driven by a negative 
acceleration signal, while the value of the nominal speed decreases, the 
output voltage of the operational amplifier 16 again assumes a positive 
polarity and the switching diode 19 is cut off. The negative polarity of 
the acceleration signal moreover ensures that the switching diode 20 is 
also cut off so that the acceleration signal can be limited neither by the 
elements 12 to 15 for limiting the acceleration signal nor by the speed 
limiter consisting of the operational amplifier 16. 
If the tool is moved from the final position back to the starting position, 
the signals corresponding to the speed of movement, to the nominal speed 
and to the acceleration have a negative polarity. Moreover, upon inversion 
of the movement of the tool, the switches 17, 18 and 23 are switched to 
the positions shown in broken lines so that the operational amplifier 16 
is electrically connected through the diodes 21 and 22 to the connection 
lead between the control amplifier 9 and the integration member 10. 
The output voltage of the operational amplifier 16 is negative and cuts off 
the switching diode 22 until the value of the negative nominal speed 
signal reaches the value of the signal corresponding to the maximum speed. 
The output signal of the operational amplifier 16 then becomes zero and 
switches the switching diode 22 into the conductive state so that the 
negative acceleration signal is also limited to a zero value and the 
nominal speed retains its value. 
It is not until the value of the negative output signal of the calculation 
member 4 falls below the value of the likewise negative nominal speed 
signal that the integration member 10 is driven by the control amplifier 9 
with a positive acceleration signal. The integration member 10 integrates 
upwards, that is to say that the value of the negative nominal speed 
signal increases. When the level of the nominal speed signal reaches a 
value that falls below the level of the negative signal corresponding to 
the maximum speed, the output signal of the operational amplifier 16 again 
assumes a negative polarity and the switching diode 22 is cut off. The 
switching diode 21 is cut off by the positive acceleration signal, which 
can now be influenced neither by the elements 12 to 15 for limiting the 
acceleration nor by the speed limiter 16.